Callista: We don't really "take" people here. If you want to use somone as an av that someone else is already using, you can. It's common courtesy in the past that you don't, but it has happened before without incident (Syren and Xilen, for example).
However it has also happened before where someone did react negatively (me and Isstal, that time Zark used MG) to another user "taking" their actor/musican/whatnot.
it's nice to ask, if you see anyone else using someone if you want. But generally, people can do as they like.
ah gotcha :) I generally do that anyway...usually I tend to look at the avatar and not the name to see who's posting...so if there's more than one with the same person in it I get confuzzled :dead