Although I'm not in it right now, and this is very odd for me, I am almost always invisible in online communities as well as on Msn and Skype and the like. I'm not trying to avoid anyone of hide from them, I just don't like the idea of being seen, although I'm aware that mods can do this anyway. It's really hard to explain but yes, I use invisible mode very regularly and it's one of my favorite features of vBulletin forums.
Aaaaaaaand with that, I'm going invisible again. x)