I am on Facebook quite a lot. I have a MySpace page but I find MySpace pretty clunky. I also have profiles on a few other social networking sites, mostly for professional reasons, but I don't use them very much.
I love Mudcat, but there are a few things that would be nice. I like the idea of having a profile where you could post as much or as little information as you want - it would help me sort out who's who! I agree with Banjiman that I wouldn't want that aspect to take over the discussion aspect, which is what makes Mudcat great.
I also wish there was a way to get to my personal page when I'm in the middle of a thread without having to scroll all the way back to the top. In between each post in a thread there are blue clickies for "Forum Home" "Top" "Post" etc. Why not "Personal Page?"
And I think getting an email when someone has replied to a thread that you are following would be good, but only if you had the option of turning it on and off for each thread. For instance, if there's a thread that's really active, I don't want to receive an email every single time someone posts. But I would love to receive an email if someone posted an answer to a question I had a couple of years ago.