Considering that the most dominant Rogue spec for PvP is the Mutilate / Prep 41/ 5/ 25, it's somewhat odd that Ghostcrawler mentions the change to Hunger for Blood as a means to tone down burst damage in PvP. Although it's a definite damage boost in PvE, it's a nerf for PvP because now Rogues have no way of clearing a bleed effect, which is physical. If only select Rogues were speccing HfB for PvP then, there'll be even less of them post-Patch 3.1.
The rest of the changes, mostly to Combat, have more of a PvE application as virtually all Combat builds are oriented for PvE DPS. That said, the buff to Killing Spree is a pretty good one, and it should be scary enough to face a Combat Rogue if you're the only one around. With the inclusion of haste to several Combat talents, I expect Blizzard to make some changes to the mechanic, as it's currently lackluster for physical DPS classes. They've said as much, so the haste-imbued Combat will get more of a buff when the improvements are worked in. Unlike most of the other classes, Blizzard doesn't seem too concerned about making all three Rogue trees equally popular or viable for PvP.
The adjustment to Chain Lightning is a clear nerf for PvP simply because it deals less burst to a single target. Never mind that the default Shaman sequence is Flame Shock + Lava Burst, Chain Lightning is the filler within Lava Burst's 8 second cooldown. Will Shamans now turn to the slower cast Lightning Bolt? We'll have to see how much of a nerf Chain Lightning will get. The other Shaman changes are clearly PvE oriented, but one change that helps a lot in PvP will be the combination of Disease Cleansing and Poison Cleansing Totems. This is good because Shamans now no longer have to choose between defusing a Death Knight or a Rogue / Hunter.
As with Rogues, there isn't much about the Shaman changes that apply directly to PvP. On the other hand, Eyonix explicitly states that they are looking into giving Enhancement and Elemental more PvP utility. I'm looking forward to seeing what Blizzard plans for this because Restoration is far and away the most popular spec in PvP, particularly in Arenas. They've got their work cut out for them.
On a good note, Warlocks are no longer the least represented class in the high rated Arenas. They've edged out Druids just barely. The bad news is, Warlocks still really suck. You know it, I know it, and Blizzard knows it. This is why Patch 3.1 will be a major patch for Warlocks. The changes they've announced so far are just the tip of the iceberg. Not much PvP-oriented changes, but the revision to Siphon Life as a buff to Corruption instead of being a separate cast spell (it's still an additional debuff, if I'm not mistaken) works extremely well for PvP. Theoretically, Haunt will refresh both debuffs.
Curse of Recklessness and Curse of Weakness have been combined -- which likely means it will reduce the target's Attack Power and reduce armor by a percentage. This will make it a powerful debuff in Arena play. Again, this is just a mere sampling of what's forthcoming for Warlocks, as Blizzard has teased that new talents have been added. Maybe we'll see more Destruction builds for PvP.
Stance dance for PvP? Yes, please. A Warrior has always been susceptible targets in PvP, particularly when in Berserker Stance. Lowered costs for changing stances should expand their reactive options considerably. While it's a tanking tool, the synergy of Rage and Power Word: Shield is awesome, and should no longer penalize Warriors who are under the protection of their (Discipline) Priest.
Other changes are simple DPS buffs, but one notable change is the rework of Sunder Armor to be more in line with all the other armor reduction mechanics. It will no longer be as devastating to cloth classes, who will no longer necessarily be instagibbed by cleave teams. It scales much better the higher an opponent's armor, though, so it's not a direct nerf. Similar to what Blizzard did for Protection Paladins, we'll probably see some PvP-oriented buffs for Protection Warriors along the way.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.