Online social networking is HUGE... but Facebook and MySpace might have some "image" issues. Take a look at Linked In as an alternative. You can find it in the "Links That I Use" on the right hand side of this blog. Another VERY useful tool is Delicious (link on the right) which is a social bookmarking tool. Both of these are free. I recommend them both.
I just found a post that gives ten ways to use LinkedIn. Go here.