The tension between PvP balance and PvE balance is once more giving the developers a hard time. Ghostcrawler has made a post on the state of the Mage, and it runs roughly as follows. They're happy that Arcane is "starting to feel like a viable alternative" to Frostfire for raid DPS. However, they're concerned that Arcane does too much burst in PvP, and they need to figure out how to fix that without hurting Arcane too much in PvE. Argh! Can we just introduce different rule sets for PvP and PvE and be done with it? The devs have been saying similar things for Rogues since LK launched: too low in PvE, but we can't make them any higher in PvP or they'll be imbalanced.
He also touches on a few more points that don't make me want to hit things. The Improved Scorch debuff is "too much of a unique snowflake" in the new buff system, forcing exactly one mage per raid to spec for it and spend a fair amount of time casting Scorch to apply the debuff (compare Winter's Chill, which is applied passively); presumably, it is going to be addressed by making it easier to apply for Fire and/or castable by Arcane and/or other classes. Making frost-based Frostfire specs competitive is also "definitely a concern, but lower priority than these other issues."
Finally (and going back to PvE vs PvP), they would like to find some way to make Frostbolt builds competitive in PvE again (the phrase GC uses is "'Shatter combo' vibe"). However, so far, they haven't thought of a way to achieve this without buffing
Cone of Cold Ice Lance [thanks, Bubsa], which they don't want to buff in PvP. Wouldn't it be simple enough to remove PvP from the game just make Lance do less damage or whatever in PvP?