Arcane has always been about mana management, and still is. There is a reason arcane has a talent to decrease the time on their evocation by half. Arcane mages are expected to use evocate on boss fights. (This is where the 2-button spam people annoy real mages... because a good mage will know how and when to use evocation.)

I recently just last week got down arthas in 10man normal using my arcane spec. I can't remember how many times i evocated, but i do remember that i casted a PoM-Mana gem during the encounter. I know I evocated at least twice, but using mana gem really helped to keep my evocation time to a minimum.

Frost has such potential... I just feel like whoever is doing the mage class just cannot for the life of them figure out how to make it reasonably viable for raiding. Currently frost is like Beast Mastery hunters... awesome utility and you can solo a lot of content and be a beast in pvp. As I mentioned above, I think the best way is to revamp frost by giving them a Freeze (ranged frost nova) spell, and removing water elemental as a summonable pet. This would then make frost a bit easier to balance.