Priest:
Holy; Good PVE (instances, raids etc), but sub-par PVP. Generally are the first targets, unless you know how to play your class. (i.e DoTs, Guardian Spirit, kiting, etc) But can survive for quite some time if you stay grouped. 1v1 they ought to get creamed by any class worth their salt.
Disc: PVE is getting better, but they still rely on Damage migation versus straight healing, so they tend to look as though they aren’t healing well. PVP is great; as they are based on migation, with enough health and resilience, they can be pretty much unstoppable.
Shadow: PVE wise they are an excellent DPS class: I myself pulled 3.7k last night in my Naxx-25 group, which some may find low, but when you consider i was using my PVP set… haha. For PVP shadow priests can be just as annoying as warlocks; we DoT everything, and then can obliterate someone with a couple well placed spells.

Shaman:
Elemental: PVE wise they are amazing! They can pull massive amounts of DPS, are wanted for Heroism/Bloodlust, and their totems are great for healers and other caster DPS. PVP Wise they are just as good; with the ability to throw down a earthbind totem, they tend to be excellent kitters. they can also heal in a pinch if need be.
Enhancement: PVE they are considered similar to Elemental; DPS is amazing, their totems rock, and everyone wants at least one shaman. PVP wise however, they were seriously lacking last time I checked. I don’t truthfully know a lot about shaman PVP, as I don’t play one outside of the 39 bracket.
Resto: Amazing healers, that can grab some amazing amounts of MP5, and chain heal is an absolutely vital spell to many AOE encounters. again, totems are nice. PVP they do really well! They can throw off fast,powerful heals, and can kite, as mentioned previous.

Warriors:
Protection: PVE is great; everyone wants a tank! Assuming you know how to play, you are always needed. PVP: not so much. Don’t really attempt. I mean, I’ve seen people attempt it, but really the gear isn’t set up for that.
Fury: PVE Dps is stellar, however it dropped last patch with the 10% decrease to damage. However, they still pull great numbers. PVP wise they can tear someone down, however really if you get caught in a battle with more than one person, you really don’t have much hope unless you have a pocket healer.
Arms: PVE DPS got a boost (Finally!) that brought them up to par with Fury DPS. They are easier, as the hit cap is also lower, which makes it easier to gear. PVP is great: With juggernaut, you can race from fight to fight, which makes it a rather decent build by itself. They have great burst damage, and they do well in AOE situations… although that really only applies to PVE.

Paladin:
Prot: See Warrior Prot
Ret: PVE: Brought up to the rest of the DPS standards, after being a joke in BC, they really do well now. PVP wise they can do well… or really poorly. A while back when pallys were seriously overpowered (they could Hammer of justice someone, a 4 second stun I believe, and then kill them before it wore off) they have gotten more balanced… but still need some work, as they are now having a slightly harder time with it all.
Holy: PVE: You are the MT healer; don’t really attempt to do anything else. Your single target Heals rock, but your AOE healing is… nonexistant really. PVP they can do really well; they can get insanely close to uninteruptable, and their heals can bring a rogue @ 31% HP back to 100% with some overheal. However, their issue is that they need mana to do ANYTHING. So, should you mana burn them over and over, they will be shiny paper weights soon enough.

Hunter:
Truthfully, as it’s a pure DPS class, im not going to do the seperate talent trees.
PVE: As its a pure DPS class, it truthfully does amazingly compared to "hybrids" (shaman, Paladin, Druid, etc) DPS wise. If you want to DPS only, then Hunters are a good way to go. PVP wise, they are still good; their pets can seriously piss off an enemy healer, and your traps can ruin someones flag running in WSG.

Warlock: PVE: Same as hunter, with some added stuff; you can summon people (always a plus) Healthstones are a great addition, and Soul Stones are godsends to new groups. PVP: don’t be the "chain-fear lock" please… they are so annoying, and truthfully they are not that effective. Except to make us all mad lol. For the rest of it, go ahead and look at Shadow priests: DoT and burn baby, DoT and burn.

mage: PVE: With the introduction of Frostfire Bolt, they now are insanely good DPS. Ahhh… I love my Mage, their DPS is like a Hunters; if not better depending on the fight. PVP: Arcane/frost really shine in this if you like to PVP solo, otherwise fire could work, as it really is a nuke.

Druid:
Balance: PVE Think a Mage. PVP wise… think a mage.
Feral Cat: PVE Think Rogue. great DPS, and they bring 5% crit to the table, so pe

When does the new World of Warcraft expansion "cataclysm" come out?