If you remember the post about the complexity of systems and player retention that I made a couple of weeks back, you'll remember that I mentioned Cynwise's excellent posts about the warlock decline. Well, here it is again reflected in GuildOx's data. Warlocks are the least played class in heroic raiding.
Warriors aren't doing much better, really. Most other classes seem fairly healthy, with classes that have healing specs doing fairly well and rogues absolutely ruling heroic raiding despite being one of the least-played classes in the game overall. It gets even more interesting once we get to look at the GuildOx spec-by-spec breakdown.