Great question Greg!
Funny but I never did get into MySpace and just finally joined Facebook a couple weeks ago. I think FB will be where I spend a little time.
It's tough to keep up with all the social networks, blogs and forums out there and still have time to work.
Here's a little summary of my social networking activities and preferences since you opened the door.
Bumpzee - Scott has done a great job with this community. I go there several times a day to scan blogs. LOVE the community although it's not very active for discussions, more for just keeping up with industry news.
New UK affiliate social network - affiliates4u - Affiliate Marketing Community. Used to be just a forum, but a very active vibrant one. Tried to get over there often.
Now that it's a full blown social network I want to get even more involved, just haven't had the time.
Mybloglog - really loved this and worked it for awhile. Here's my community.
5 Star Affiliate Programs Blog - MyBlogLog
216 friends and
OOPS 86 admirers waiting for approval. See that's the hard part. Keeping up with all of the activity at each one.
StumbleUpon - really wanted to hit this one hard and get active just to drive traffic. Never had the time. So now I just
BUY traffic there. Worth it for 5 cents a visitor!
Facebook - even though I'm new there, I like it and hope to spend more time there. I'm in Shawn's affiliate marketing group. Haven't had time to look around to find others.
Blog Catalog and Spiceypage - can't keep up with those 2. Keep getting friend invites from people that I don't know that don't really seem to be in the biz - so have had to let those 2 slide.
Myspace - think I've only been there 3 times. Once to Shawns and twice to Stephens Top Affiliate page. It just never grabbed me. Guess I'm too old!
Linkedin - one of the 1st big ones, but I never got into it and actually get really frustrated with it because I just got so many invites that it started to be an annoyance. Now I just ignore them all. Terrible I know. STOP SENDING ME LINKEDIN INVITES!

Wish I would have accepted them all now. Would have tons of friends. But just never really liked Linkedin much.
IF I HAD an ASSISTANT which I'm always thinking about adding, I would have her spend lots of time just approving friend requests at all the networks because I dont have time to keep up with them all.
So what about everyone else? Which ones do you like and where do you hang out?