One of my favorite things about professional theatre (in my experience so far) is that you aren't required to greet audience members following each show. Don't get me wrong, I believe very strongly in thanking the audience and receiving them -- but in structured opening and closing receptions, and not in costume. I love the idea of leaving the character with each audience member rather than involve the work, emotions, and disposition of an actor in the encounter. Community (and especially children's) theatre is a bit of a different situation, so these are just my feelings regarding professional theatre...and the training grounds for it (aka college!).
GO FOURTH WALL!
EDIT: I know it's been a year since this post, but I'll add a link to another local blogger's take. Apparently, Broadway is increasing the talkback idea, which I think is an awesome way to augment actor-audience relationships. One idea included texting opinions and questions, so a degree of anonymity could remain -- cool thought!