Do GMs ever appear in game?

Q u o t e:
When I played Ultima Online as well as Everquest there were time where GMs and Guides would appear in game. Does this ever happen in WoW?

Our In-Game Support staff does certainly enjoy face time with players, although when we have high ticket volume, it's unfortunately just not practical for Game Masters to spend a lot of time showing up in-game.

Still, there are some rare opportunities and situations where Blizzard staff will go into the game world to check up on things. We tend to stay invisible or low-key to avoid disrupting the game environment when we're working, but have been known to set off the occasional firework when we find an appropriate place to appear to players.

When Blizzard employees appear officially in-game, we tend to wear some signature robes and a special icon will appear next to the GM's name in chat messages. More info on official GM appearance can be found here:
http://us.blizzard.com/support/article.xml?locale=en_US&articleId=21261