I leveled 65-80 with 3x mage, priest, druid and I was arcane the whole way and never even considered another option. I am now farming heroics with this team and my 3 mages are still arcane and not looking back.

70-80 I only used 2 buttons on my mages:
Code:
/castrandom [target=focustarget] arcane barrage, fire blast
Which pretty much Gibs any non elite target just by mashing this button til your out of combat :P The best part of this macro is all instant on the run damage. No stop and cast slowdown
Thats also one of the few buttons I use in BG's. I easily rack up 1600-2000 honor per BG (honor on the right side of BG scoreboard) just using this button and playing smart.

&

Code:
/use 13
/use 14
/cast arcane power
/cast presence of mind
/cast arcane blast
This of course was recently nerfed to not work as it used to. PoM+Arcane Power now have a shared cooldown that in all honesty just works weird.

Now at 80 I added a boss killing general DPS macro:
Code:
/castsequence [target=focustarget,nochanneling] arcane blast, arcane blast, arcane blast, arcane missiles
I manually use Presence of Mind for a 4th Arcane Blast right before Arcane Missiles goes off in my castsequence macro whenever PoM is up and use Arcane power in a "things must explode" macro with my trinkets and any other appropriate cooldowns.

1 of 3 mages has slow at the very start of his cast sequence and then ABx3, AM, ABx3, AM I *think*. I'm not at home so I can't check right now,
either way it works to keep slow up almost 100% of the time without refreshing it too often and losing to much DPS. This way all of my mages then benefit from torment the weak and 12% increased dmg.

I stayed Arcane mainly because of the amazing damage it does in 5 mans (I have seen a solo played arcane mage break 6K on the mammoth boss in Heroic Gundrak but he is much better geared than I am and had Heroism which I do not in my team.
Also I don't like the on proc instants in fire/frost. The fire tree's instant pyroblast and frost tree's instant fireball are both great DPS adders solo but boxed I find them to hard to utilize as accidentally casting either of them do to a missed proc is a huge hit against your DPS. Arcane's proc damage is missile barrage and you do not lose much to cast a normal arcane missiles if you miss the proc.