The Arcane tree as it now stands is heavily item-centric. Arcane mages do an insane amount of PvE damage at the top end, but that is due in large part to the use of the Mystical Skyfire Diamond, the Lightning Capacitor, and the two-piece set bonus on the Tier 5 set. When Patch 2.3 rolls out the MSD and the Lightning Capacitor (I have yet to see documentation on this, although they say it's in there somewhere) will both receive significant nerfs, which greatly affect Arcane mages. As Adultralisk mentions, being reliant on carrying around 2/5 of Tier 5 will only work for so long. As guilds progress, mages will be moving on to Tier 6, and when WotLK arrives, T7 and T8. Why, therefore should Arcane mages be expected to carry out-of-date items simply to receive 20% additional damage to their Arcane Blast?
One very intuitive suggestion to this problem came from a commenter named Rounced. He suggested that Arcane Blast be changed, and the T5 set bonus removed. If the debuff duration of Arcane Blast is increased, from 8 seconds to 11 seconds, while its damage and mana cost reduced to 8%, this still gives Arcane mages time to cast Arcane Missiles in between blasts, while keeping the spell from being overpowered. Other posters suggested adding a spell haste talent to the Arcane tree, thus removing the reliance on the MSD's proc.
On the PvP side of things, Mages are concerned about the increase to Hypothermia. They say that with that increase it is now pretty much impossible for a mage to Ice Block twice in an arena battle. When Hypothermia was added to the game initially, it was seen as a pretty big challenge, but one that mages adapted to. A small part of me wonders if they will be able to adapt to the 45 second wait time now, but I realize that 15 seconds is an eternity in PvP.
The other point made was that there is only one PvP spec for mages currently, and yet three trees that would love to use their abilities in the arena. We had heard from the devs that they do not intend every spec to have viability in every aspect of the game, I hear you. But mages still would like to have some survivability added to the other specs as well. Someone in the thread suggested a limited Ice Block being added as an ability rather than a talent.
My point is, there are a LOT of great suggestions in this thread, and any mage interested in the future of the class after the patch should spend some time to read it. Perhaps you have a suggestion as to how this issues might be improved, and can add your voice to the discussion. There isn't going to be a change anytime soon, as far as I can tell, that's just not how the devs work. Adultralisk himself states that he isn't looking for an instant fix, but an eventual one, even if you have to wait until the next expansion, would be more than welcome. But perhaps enough intelligent discussion on the topic will raise the issues in the devs minds for future changes to the class.