I've been on MySpace for a while, and have found it pretty useful for making contacts. Plus it's fun to personalize your site and add a little flavor
As for LinkedIn I've just joined and am still getting the hang of it, same with Affiliates4U. Bumpzee is one that I've been meaning to have a look at...
I totally agree with Linda's comment about the time issue - there's a lot to get from these networks, however to make the most of them you really need to invest the time.
