Personally, I prefer more forums then social networks. But my vote will for also for facebook in 2009.
Facebook didn't work out as well as I'd hoped, I'm still working on it but Twitter definitely was the winner for me, I'd give second place to stumbleupon.
StumbleUpon easily has to be my best. I've gotten over 3,000 visits to just one article of my blog from them, they really run a great social networking site.
I have just begun social networking a few months ago and I think twitter is so much better that facebook
I think having created your own Social Network is well worth it. I don't do a lot of facebook, myspace, etc. Really don't have a lot of time for them is the main reason.
Personally Face book is the Best Social Networking Site with more than 65 million active users and it also has many inbuilt features.
Myspace's turned into a place for girls who takes photos in front of mirror. Facebook has a real community to make marketing wishes come true.
I use Onlywire to submit new articles from my blog to a bunch of /social sites, you have to go in each one and set up an account but it's worth it for the backlinks.