How to gear Prot in WotLK?

[Twoflower]

This is what distinguish dps-making-their-queues-shorter tank from "real" tank. It also define the way you are going to level up, since dps tank will never be able to go to instances with significantly higher mobs than their current level.
I have leveled between 65-70% of WOTLK in instances, never staying in a single instance for more than 3-4 times. That would not be possible for dps tank because he will have crap hp, will be crit-able and crush-able (this is impossible to avoid for a while aspecialy when starting lvl78-80 instances where bosses are either 82 or some are even boss-types.
Gearing appropriately also makes healer life a lot easier, which is very important for smooth runs especially at start of WOTLK where most healers still run in TBC quest items and random green drops from their short experience in Northrend. It is not necessary to go overboard with this but the initial tanking set is worth no more than 60g in mats (40 cobalt bars is more than enough to craft full set). Cobalt gear will ensure you are crit immune at least till level 74 if not more. You can start picking quest rewards on the way to increase your survivability further. Incorporating Saronite pieces as you level up into your gear will ensure you are perfectly equipped to tank all the way to 80--for total amount that should not exceed 500g in mates and craft fees.

I played my warrior as a tank from level 60 all trough BC and wrath, never did anything but instances. I did so in prot spec and in proper prot gear. I can tell you : it was a waste. You dont need a "real" tank for leveling instances. Dont you get all "real tank" on me.

Crap HP are still enugh for crap leveling instances. You can tank anything up to halls of stone with less than 15k life, and you can tank wotlk heroics with 20k life. If you remember 1 year back, that was actualy the norm. The instances have not changed since then. Being critable is no biggie in leveling instances, it is just a bit more for your healer to heal trough. And crushing blows no longer exist, in case you were wondering.

Prot gear is ok if you have it, but it is no biggie if you dont have it.

[Baron01]

I played my warrior as a tank from level 60 all trough BC and wrath, never did anything but instances. I did so in prot spec and in proper prot gear. I can tell you : it was a waste. You dont need a "real" tank for leveling instances. Dont you get all "real tank" on me.

I have leveled paladin, death knight and warrior tank to 80 and still play them. I believe I have enough experience to go "real tank" attitude in topics like this. Prot gear is not necessity but it is great help, especially with introduction of BOA gear, RAF service and all the adjustment to leveling speed made by Blizzard. The ease of leveling is causing people to run in gear several levels below currently available gear. It is not rare to see 68-70 characters in UK or AN with gear from Hellfire Peninsula quests. This is the situation where real tanks who put some effort into their gearing and play style really shine. Doing that little bit extra to actually perform at the best of your capabilities can give players well deserved satisfaction. And it does not cost a dime these days, as I have said in my earlier post. All the prot gear you need at lvl70 wont cost you more than 60-70g. That is very good price to make you a real tank.

Crap HP are still enugh for crap leveling instances. You can tank anything up to halls of stone with less than 15k life, and you can tank wotlk heroics with 20k life. If you remember 1 year back, that was actualy the norm. The instances have not changed since then. Being critable is no biggie in leveling instances, it is just a bit more for your healer to heal trough. And crushing blows no longer exist, in case you were wondering.

Low health is not an issue if you are properly geared. It might not be an issue even if you dont use protection gear but why taking the risk. Why forcing other players to cover up for your laziness?
I dont want to break it on you too hard but crushing blows do exists, they are just not an issue in end-game raiding anymore. You are also mixing apples with pears because defense rating by itself was never able to negate crushing blows. It was the combination of avoidance and mitigation stats that have pushed crushing blows off the hit table. They were removed from end-game raiding long time ago due to change in mechanics that triggered them. Crushing blows can only occur when you are hit by a monster 4 levels higher than you. Boss-type creatures are considered always +3 levels to their target hence you dont need to worry about crushing blows when you go toe-to-toe with nasty dragons, animated abominations or even Lich King himself as lvl80.

[Paff]

You can pretty safely follow wowhead's preset protection stat weighting scale to make gear decisions for leveling through dungeons. It tends to overestimate block value and rating irrc but that's totally okay for 5 mans. Trust me, you will notice those holy fires, lava bursts, out-of-tree-form starfires from your healers and even meleeing holy paladins. Also i would recommend getting Argent Crusade tabard as soon as possible (77?) to start building your reputation in high level normal dungeons for your head enchantment, as you will need it later anyway. Fill rest with leatherworking stamina patchments, if you wish so. Generally you will need nothing more than blue drops to feel good. The only problem is trinket slot, as there's only one tanking trinket available in normals. And that's how you became a jewelcrafter.