PvP - Arenas
Burst Damage
We think this was a bigger problem when season 5 started than it is now. We managed to address some of the worst burst (Bubbled Ret pallies, Arcane Barrage, Mutilate+stun+stealth, Explosive Shot, Impurity + Howling Blast, and now finally Shadowfrost Icy Touch). At the same time, being able to call upon your burst when needed (blowing cooldowns etc.) is pretty important for being able to finish someone off before they can escape or get a heal. We won't have a very fun Arena if everyone is always hitting for 2000 damage (they just can't be hitting for 20,000 either).

We have seen many fights now that won't wind down because the healers can just keep going and going forever. While we don't want fights to last for 6 seconds, we also don't want to see the only way a fight can end to be through mana drains (the spell effect itself, or just slowly, painfully watching someone's blue bar exhaust itself). Ideally both situations would sometimes occur, but there would also be more fights somewhere in the middle. (Source)

[...] We definitely designed a few classes originally in a way where all they bring is big burst. We have realized now that this doesn’t work. It ends up being not fun for the burster or the burstee. We are trying to redirect Ret, Arcane, and PvP rogues of all types away from the proverbial “two shot” and more towards having different answers for different situations. (Source)

Paladins and Death Knights too dominant
We think DKs and Holy paladins are too dominant in Arenas. Beyond those two there are some imbalances, but you are going to find a lot of debate among the community about who it is, and I think that might come to dominate the rest of the thread. The "two-shotting" is a little exaggerated in most cases. (Source)

Resilience
You don't need 800-1000 resilience to survive a Shatter combo. The game is designed around the notion that you will escape or prevent CC. You aren't going to survive long CC'd with players beating on you no matter how high your resilience is.

I think what we might do differently next time is make higher resilience values available earlier. You start to notice resilience having an effect at say 500 or so and you start living long enough to counter attacks at 800 or so. A lot of players going into the season with 100 or so resilience did get blown up. This felt particularly weird because:

1) For the last few seasons, their resilience had pretty much just gone up. Season 5 was a reset that had a lot more in common with Season 1.
2) In addition, this was complicated by the issue above -- that players were combining the weak resilience with very potent PvE weapons that they had already looted from KT. If the Arena season had started around the same time Naxx had opened (combined with slightly better tuning on Naxx) then there would not have been such a discrepancy.
3) Some classes had overly powerful built in resistances that made up for the lack of resilience. Specifically, DKs had a lot of cooldowns and passive defenses built in for tanking and paladins had their shields, which could be used offensively at the start of the season.

To drag out a tired cliche, the combination of these 3 (low resilience, KT weapons and baked-in defenses) plus the high burst at the start of the season created a perfect storm for fast Arena deaths.

Perhaps a better solution is to have relatively high resilience on the starter gear (like 500) but at the cost of offensive stats. We do want PvP gear to be a progression though. We don't want you to start the first season of an expansion with amazing resilience and offenses. (Source)

Raids & Dungeons
Converting Emblems of Heroism to Emblems of Valor
We don't have any current plans to allow emblems of heroism to convert to emblems of valor. (Source)

Progression Path
We consider 10 and 25 separate progression paths. Here are different ways to raid:

A) Heroic 5 player -> 10 player Naxx -> 10 player Ulduar -> 10 player Ulduar hard
B) Heroic 5 player -> 25 player Naxx -> 25 player Ulduar -> 25 player Ulduar hard
C) Hybrid. You focus on A but sometimes pug B, or focus on B but run A on off nights. The one possible exception could be that if you are just stuck on 25 Ulduar hard, you can get upgrades by running 10 Ulduar hard if you are up to the challenge.

If we made a mistake in LK, it was that path B was too easy. That meant that A felt like a waste to some players because the loot was inferior. We think it will work better in Ulduar. (Source)

25-Player content difficulty
We have positioned our 25-player content as more difficult and therefore capable of generating better rewards. Managing a group of that size requires a little more effort and we figured if the rewards were the same, we'd steer pretty much everyone towards 10-player raiding. At this point we don't want to do that. The confusing part is that the 25-player content in Lich King ended up being a little on the easy side compared to the 10-player content. Players viewed the 25s as puggable which then made the 10s seem optional since the rewards weren't as good.

If anything we think the 10 version in Ulduar will end up a little easier and more puggable. We'll probably see 10 and 25 Ulduar pugged eventually, but it might not happen right away. Let me add that if you just love 10-player raiding and are up to a challenge that we do have 10-player hard modes and the loot available there is superior to 25-player normal. (Source)

25 Players vs. 10 Players raiding
I understand your point on the 25 loot being of higher item level. However we explored this issue quite a bit and I still believe that some non-trivial number of players just prefer the larger raids. How can that be?

-- They like the epic scale of it requiring an army of players to defeat a boss.
-- They like the power mulitiplier. You generally do more damage and healing in 25 because you have more buffs. This feels cool.
-- They like the encounters designed around larger groups. What I mean is that in a 25-player fight we can do things like just randomly kill players or isolate them in small groups. They like sometimes having to employ 4 tanks at once. It is hard to do these kinds of thing to 10-player fights.
-- Their guilds were formed back in the day of exclusive 40 or 25 raiding, so that is the group of friends they have and how they have built their guild. They just think of the politicial nightmare if they have to split their guild in two.

So for those reasons, and a few others, we think the smartest design is still just to let players decide if they prefer 10 player raiding or 25 player raiding. Some have a small group of friends and want to not have to put up with the weak links or undependables. They like the pressure it puts on every player to perform. Others have large, social guilds and like to assemble 25 players together. They may be more tolerant of being able to bring the 25th player along even if he isn't stellar. They may like all of the reasons I mentioned above. It's just a preference, just like Horde vs. Alliance is a preference. (Source)

"Hardcore" elements of the game
Our goal has always been to make the game as accessible to as many players as possible. Our game is influenced by what we've learned from both our successes and our mistakes. Some of the "hardcore" elements of the past that some players think they now miss weren't even necessarily intended to be "hardcore", but rather ended up that way because a better way wasn't yet available.

Engineering
Developer Q&A (Source)
1. Could we have some elucidation of what perks engineering has that in the developers view "work out compared to what other classes (sic) have"?
The perks are the glove enchants. The armor increase on the gloves should about match up to what stamina would be there instead, the haste boost can be really useful on some classes (whether it's just faster healing or faster damage), and the damage from the rocket launchers should be about equivalent to the dps boost that perks from other professions provide.

If we wanted the perks for every profession to be the same, we would just add 50 stamina for having one profession and then 50 attack power/spell power for having another one - but we would rather keep the perks a little more unique and fitting for each profession.

2 . What is the problem in providing a drop for goggle upgrades? (doesn't have to be BIS, we'd just like goggles that are ballpark competitive).
We don't want to provide really good and/or best-in-slot items that you upgrade throughout an expansion. We kind of set a precedent for this in The Burning Crusade, but we weren't happy with it so we are trying to get away from it now.

3 . Whilst the mote extractor was finally a means of making some money in TBC, the pretty much universal view of engineers is that as a help to get money in WOTLK it doesn't work pretty well. Can we swap Northrend motes for something cool to drop in Uldaar in 3.1.x?
This can probably vary a bit depending on the demand from one realm to another. We think it is okay as it is for the time being.

4. Do the developers have plans to seriously review engineering in 3.2?
There are no plans for an overhaul if that is what you mean, but we will continue to watch all professions and make changes as we feel they are needed.

5. Is there ever any prospect of some of the vanilla Wow favourites like the MC caps (with strictly no arena caveats) capable of being used again?
Items like the mind control cap would not be usable in Battlegrounds or Arenas. Balancing an unbalanced item is extremely problematic if not impossible. There is a much greater possibility of toy items that don't provide an extreme advantage or have crazy scaling being updated than something like a mind control cap.

There is always the possibility for more changes and tweaks to how things work, like removing an activation effect from the global cooldown and such, but this profession is especially challenging to balance between PvP and PvE. There are quite a few high level PvP players that use this profession because of the extra burst it can supply, so if you feel the damage is not enough, it is difficult to just increase the numbers when it is already powerful in PvP.

Lightning Gnomish Generator damage nerf
The burst was higher than we wanted, we lowered the burst but put passive crit on the item. (Source)

Classes
Changes postponed for the next patch
I am not sure where you get your information, but do yourself a favor and cut them off. There weren't any class changes that didn't make it into this patch that are now being planned for the next patch. Class balance changes just don't work like that.

If you're referring to the hunter ammunition change, that's not quite as simple as just a "normal class change", and we decided to wait on that because we have some cool plans for how we're going to design the change.

Delay before classes balancing
We are more quick to balance in LK than we were in BC. However, as a counterpoint, you can find plenty of posts by players who feel that they have whiplash from too many changes. We need to evalaute carefully when we think a change is warranted and keep both extremes in mind. (Source)

Priest (3.1 Skills List / 3.1 Talent + Glyph Calc.)
Power Word: Barrier (Group version of Power Word: Shield)
I thought the disc priest group bubble thing got pushed back? Did I hear wrong?
No, we decided against that change completely. We were considering a "power barrier" for discipline 3.1.0, as we do think it's a really cool idea. With that being said, it's not something currently on our to-do list, but it's possible we could revisit the idea somewhere down the road. (Source)