I have no idea what I'm talking about really, but every time I've noticed a mage's DPS stand way out I've asked them about their spec.  And since the armory came out I've been able to take a look at the mages I've admired most.  While I've seen some fire mages do a ton of damage, most of the damage dealers I've really noticed are frost.  Maybe that's simply because I want to have a frost mage someday so I watch them more closely, I dunno.

The thing that has really surprised me since I started checking the armory is that most of the frost mages who I've admired actually have more points in arcane than frost!  They seem to take all the arcane points that would compliment the frost talents.