I've only been doing the forum / internet thing since 2002. I've joined forums on the basis of my interests at the time, but even if the interests stay strong, I get bored with the forums themselves.
Currently I'm on a few harp related forums, but not super-active. I'm a member of LiveJournal, but don't keep a page for myself, just check a friend's page there.
Being active on UK-Y is important to me because I need to stay up on all of the quickly changing stuff that's going on with visas, citizenship, etc and because I really like a lot of the people who post on here and have now met a few in person as well.