Professions
Increasing Nitro Boots duration to 5 seconds
That is an option we may explore. We also have several other changes to Nitro Boots in mind. We may include additional stats to making this comparable to other boot enchants. Many ideas are currently on the table and we are narrowing them down to the very best. I hope that not too many of my fellow engineers dropped the profession because of this change. Cool things are on the way. Hang in there. (Source)

Player vs. Player
Water in arenas
There used to be an effect on Arena water that prevented it from really kicking in until about 4 sec or so. Somewhere along the line that stopped working, but our intent is to get it working again.

The buff was mostly so casters didn't have to spend so much time on regeneration in between pulls or when soloing. If we had not buffed Arena water, then mage water would have been too good, and if we had not buffed mage water, then a core mage ability would be bad. The solution is to make water work like water, but make any water less uber in Arena. (Source)

Consequences of nerfs in PvP
In PvE, if we nerfed a class by 5%, you might find that the class representation drops slightly. In PvP it’s a whole different ball game. Teams may choose to use other classes. Players who were dps spec may choose switch to healing. If a class is nerfed, the class it countered may suddenly rise. Balancing classes in PvE is like adding or removing helium from a balloon. You can make it go up or down a little. In PvP, all of the balloons are connected together through complex webs and you’re doing the tweaking in a wind tunnel. That’s not a cop out saying that PvP can never be balanced, but is instead my counter to the argument that “because spec representation rises and falls to such a degree that the changes are too extreme.” Even small changes can have extreme results in PvP. (Source)

Itemization
Regen Stats
The solution here, from our POV, is not to take the regen stats off of gear, but to get you to care about them. To us, that's the same argument as saying "I can get all of the hit I need through talents, so hit on gear is a waste for me. Please remove it."

Using Leather armor instead of Plate as a DPS
I addressed this recently. The root of the problem is that putting AP + Strength on plate feel dumb (because except for block, it's the same thing). Putting Agi + Strength on plate feels useless. A long-term solution would probably be something like letting rogues (and similar classes) derive AP from 2xAgility and just put Agi on leather and Strength on plate. (Source)

Dungeon itemization and badges
I'll just comment on one point you made. In BC we felt like the system pushed players too hard into running the 5-player heroic instances long after they could benefit from the gear in order to farm badges. In LK we totally did away with this (since badges themselves are tiered) and also got rid of attunements and made Naxx relatively easy. As a result, I agree that we let end-game focused players graduate from heroic 5-player instances too quickly. In the future, we'd like to strike a more even balance where it might make sense to run a 5-player dungeon on a non-raid night, but you didn't feel obligated to every night. (Source)

Classes
Spellpower Cap?
At this point in time there is no cap on spellpower nor do we intend to introduce one. (Source)

Dual-Spec
The purpose of dual spec was not to make talent choices irrelevant (because you'd only have a talent in the cases where it was most useful). The purpose of dual spec was to make it less painful in those situations where you often switched between two commonly-used specs. This is the reason we placed so much emphasis on remembering action bars and less emphasis on the gold-saving aspect of the respec.

You won't see more than two specs for a long time, if ever. Let's see how the first one plays out for more than 6 weeks first. (Source)

Tanking in PvE
Traditionally, bosses hit almost entirely through physical damage and then occasionally threw in a big magical hit. The magical hits were scary because they couldn't be blocked and went through armor, so the only things you could do about them was burn a cooldown or heal like crazy. Fortunately the magical attacks cannot crit so at least the damage, while large, could be predictable.

Block was a fine stat back when bosses could do Crushing Blows. In their absence, it does feel like it has slipped as a source of mitigation. We (the developers and the community) were worried at the launch of Lich King that block would make warriors the best tanks, paladins second, and everyone else far behind. In retrospect we should have been more focused on the cooldowns and number of hits a tank could take in a row. (Source)

Balancing PvE encounters for each class
You know, those encounter designers are right across the hall here. I am waving at them right now. We all work pretty closely together to match the boss abilities to class abilities. We work even closer together on the numbers. When someone is tuning Frozen Blows or Imbalancing Strike, they do that knowing what the stam pools, mitigation, avoidance and cooldowns are of appropriately geared tanks.

That's not to say boss design is irrelevant. Say for example we made a raid with one boss, like Eye of Eternity. Now say Feral druids were slightly better at that fight. Does that mean druids are overpowered for that encounter?

There are 14 Ulduar bosses. If DKs are better at tanking 5 of those does that mean DKs are overpowered? If the next tier of content has bosses that druids are better at tanking, does that make things equal?

We want them to all be close ideally. Since we don't want to give every tank the exact same stats and gear they are never going to be 100% equal. The trick is discovering how much of a delta is too much (and it's an answer that's hard to generate with math alone). (Source)

Death Knight (3.1 Skills List / 3.1 Talent + Glyph Calc.)
Making Dual-Wield DKs viable
Next major patch. (Source)

Hunter (3.1 Skills List / 3.1 Talent + Glyph Calc.)
Hunter DPS and scaling
Hunter dps was where we wanted it to be in Naxx. Two problems arose in the Ulduar tier. First, we improved the dps of other pure classes, especially rogues. We have a small change coming up that should slightly improve hunter dps to make up for this and will apply to all level 80 hunters. (But do not assume you are going to see a 20% dps jump when we make this change.)

The second problem is that in order for hunter dps to improve, they must upgrade their bow and arrows. A rogue by contrast needs two weapons and a Ret paladin one weapon. However, a higher tier of arrows was not available anywhere. Because dropping arrows as loot feels cruddy, we handled this in the past through a rep grind. We can't just give the arrows away to fresh level 80s or hunter dps will be too high relative to other classes. Long term, we have a different solution for arrows, but that won't help in Ulduar. So the change we made was to let bows (and guns) scale more than other weapons to make up for the "missing" ammo. The ammo is baked in to the weapon damage.

We didn't think this was a problem for the 10-player case because the melee and casters are not getting weapons with such large stat increases. The Ulduar 10 loot is slightly better than the Naxx 25 loot, but only slightly (it depends a lot on how many 226 items you were able to get). Since we said Naxx 25 wasn't a problem (in our eyes), Ulduar 10 isn't a problem either. (If you think your Naxx damage was too low I can understand how you might feel differently, but that is not our position.)

Players have a tendency to sometimes invoke "scaling problems" as a generic explanation for why they need buffs. However, in this case it was truly 100% a scaling problem. Scaling problems only happen when characters acquire better and better gear -- literally as gear stats increase, some classes might not be benefiting as much as others so balance at one tier goes away at higher tiers. The weapons in Ulduar 25 with their relatively large stat increases had this problem. The weapons in Ulduar 10 with their slight or null stat increases did not (though they will in the next tier of content, as will the Ulduar 10 hard mode weapons). (Source)

Priest (3.1 Skills List / 3.1 Talent + Glyph Calc.)
Past priest changes
I went to extraordinary lengths to communicate with priests after the Circle of Healing nerf and the mana regen nerfs. We listened. We made some changes that came directly out of some of those conversations. Improving PoH and the hymns, making Disc a more legit single-target healer, giving priests ways to improve Renew and CoH, all came out of those discussions. They may not have been the exact changes you wished to see or perhaps you think we didn't do enough, but that is always going to happen with something as subjective as game design. We ask that you not confuse "You designed my class differently than I would have designed it" with "You never listen to us" or "You don't care about us."

We understand that emotions enter the picture when you're talking about your character. But what will always convince us are sound, logical, clean arguments that appeal to balanced and fun gameplay. (Source)

Shaman (3.1 Skills List / 3.1 Talent + Glyph Calc.)
Renaming totems to fix totem stomping macros
If the solution was that easy, we would have done it long ago. (Source)

Cool things are on the way. Hang in there.