Shaman
There were so many changes for Shamans this patch that they all got free respecs, something that Matthew Rossi's certainly enjoyed (as long as he could play his character, that is). Elemental is my favorite spec, and it's pretty much how I played my shaman 90% of the time, the other 10% being Restoration. Fortunately, Patch 3.0.8 improved Elemental, so we should see a significant improvement to Elemental Shaman performance both in PvE as well as PvP.

On a basic level, Elemental Shamans should be dealing more damage now with better scaling through Shamanism. I've been hit by a 7k Lava Burst before the patch, so color me nervous the next time a Shaman hits me with a Flame Shock. One key talent that will have significant impact in PvP is the rework of Elemental Mastery. The old effect of a guaranteed crit was important to PvP. The new design delivers higher sustained throughput in raids, but makes it less reliable as a finisher in combat.

Elemental Warding has become more valuable, and its location in the tree makes it accessible to more builds. It definitely contributes to better survivability. We'll see how Elemental Shamans perform post patch, as the most popular spec for Shamans in Arena play is currently Restoration. Elemental no longer provide the frightening burst they used to pre-Wrath, which was critical to old comps, and the change to Elemental Mastery hurts that even further.

Overall, however, Elemental got a tremendous boost this patch, as raw damage is still damage. They also have one of the best self-peels in the game with Thunderstorm, and have decent survivability. Hopefully, we'll see more Elemental Shamans represented in Arena play, although I've quite had enough of them knocking me into the abyss in Eye of the Storm.
Warlock
Unfortunately, Warlocks still suck in PvP. I can actually end my assessment of Patch 3.0.8 right there, but I'll be a little less harsh and say that Demonic Circle can now remove snares and that Demon Armor now grants a pretty good amount of armor. Survivability is a bit higher, although they've fixed the Dalaran sewers so Warlocks can no longer teleport back into the sewer pipe. Mana drain mechanics were also changed to percentages, so that means Warlocks' Drain Mana is no longer the worst draining spell. Hooray!

What else? Well, Glyph of Turn Evil has been nerfed, so you can use Metamorphosis just a bit longer against those pesky Paladins. Oh, but the best news from all this is that demons are a lot tougher now. This is a brilliant change and will contribute greatly to Warlock viability in PvP. That said, the class still sucks right now and will have the lowest representation in Arenas until 3.1.
Warrior
Titan's Grip is OP. I know it, you know it, and even Blizzard knows it. Although Warriors are pretty much middle of the road now in PvP, they still do rather well in all Arena brackets. The only thing that kept all Warriors from speccing down Fury in PvP was Sudden Death, which gave frightening burst potential in PvP. The talent was nerfed considerably, but still provides great burst, so we'll continue to see an even mix of Arms and Fury Warriors swinging their weapons in Arenas and Battlegrounds.

Bladestorm's immunity to crowd control is probably the only thing that's keeping PvP Warriors from re-speccing to Fury, even with the hit penalty removed from Titan's Grip. Bladestorm and the MS-effect of Furious Attacks should keep Arms Warriors as Arms and Fury Warriors as Fury. Overall, it's still too early in the season to see which classes need to be balanced (except for Death Knights and Paladins, that is), but Warriors, as always, will be a constant force to be reckoned with.