Why are rogues the least played class?

This is a topic we discuss a lot. We don't believe it has anything to do with game balance though. Rogues were also less popular than other classes at times when they consistently topped damage meters and dominated PvP. This isn't a trend that seems to rise and fall with current game balance. Overall, we've never seen a strong correlation between which class is considered overpowered and what players are playing. (Note: This is true overall, but if you move to smaller and smaller sample sizes, perhaps Arena teams above or below a certain rating threshold or raids above or below a certain level of progress, then you can see some correlations between power--real or perceived--and popularity.)

We do know that a lot of rogues appeared to reroll DK, at least when the class was first introduced. We also think rogues were more popular back in the day before flying mounts and instance-teleportation, where ganking someone out in the wilderness was more common. We saw a surge in the popularity of hybrid classes, especially druids and paladins, as running heroic dungeons became something nearly every player did instead of a more dedicated minority.

It's possible that some rogue mechanics aren't as fun as they could be. This is a really subjective issue though, and it's trivial to find members of every class and spec declaring that their character is clunky and ill-conceived while some other class or spec appears sleek and shiny. We made some changes (i.e. stealth movement speed) to try and make some of the rogue mechanics more fun and this is the kind of thing we'll continue to keep an eye on.

Plenty of players love rogues though. We don't want to give the perception that the class is dying or anything like that. It's just less commonly played than say paladin, which is probably why you see so many paladin-related threads on all three forums.