Vhiari has released some interesting stats about the Arena Tournament realm over on his Blogspot site. What he did is take the top 5000 (due to "Armory limitations," he says) personal ratings in each bracket, and then charted them according to classes. Keep in mind that this is the Arena Tournament realm (the live realm data is also available separately), so this is more an indication of what players are doing so far on the tournament realm rather than class viability in day-to-day situations.
But keep in mind also that Blizzard is watching the Tournament realm closely for PvP balance, so what we see here could have some hints into the future of Arena changes. Mages especially don't make out too well on the 5v5 chart, and Hunters don't appear to fare much better. Warriors, as you might expect, are off the charts, but comparably on 5v5, Druids aren't at that level. Rogue placement is a surprise, too, but Vhiari just says in the comments that that's more an indication of how many people rolled rogues on the TR rather than a signal that Rogues are rocking 5v5.
Interesting stuff. Unfortunately, the data is a little too fuzzy to pull off any serious conclusions (even if Mages aren't getting high ratings, this chart does nearly nothing at all to help us figure out why that might be), but it's an interesting look at what's happening on the TR so far.