You have to be real careful about how you put together statistics. As Gregg Easterbrook said, "Torture numbers, and they'll confess to anything." So, grain of salt, people. That being said, Arena Junkies has put up a pretty interesting compilation of numbers. They took a look at their (fairly substantial) membership, and figured out the approximate class makeup of each Arena season's Gladiators.
The results aren't exactly a surprise, which supports the analysis's validity. Warlocks -- once the Arena juggernaut to the sounds of much QQ -- have lost 8% of their dominance in the Gladiator ranks. By comparison, Rogues have picked up 6.5%. Druids are the big winners, though. Only 7.5% of Season 1's gladiators were druids, compared to 16% of Season 3's. And yeah.
There's a lot of metagame interpretation that could be done regarding these numbers. Melee have slowly risen in power over the span of three seasons, and Paladins -- once the bubbling unstoppable -- have really dropped in performance. Druids used to be unremarkable, but now the "science" of Line-of-Sight and Mobility has taken the day.
Arena Junkies promise to further update their analysis when the Hall of Fame is updated for Season 3. But I agree with Tyveris: I think the current sample is indicative, and we're not going to see any huge differences between these numbers and those.