Lou Susi

Both. I join as many social web sites as possible for a few reasons:

1. As a User Experience Design Professional, I need to keep up-to-date with all the latest Web 2.0, Ajax and social webbedness that's 'out there'. So I join to see what experiences are valuable and what interactions or member populations seem to create the most exciting, new concepts and online communities.
2. I feel you need to get 'out there' and manage your brand as much as possible. Even if you just park an account with your name on it, that's taking ownership and preventing someone else from invading your GoogleSpace.
3. The social web seems to weave and tangle and play in a way that brings more and more people to any other 'real' websites or experiences you might have been involved with designing, developing, etcetera.
4. To check out the limits of these experiences and see what you can and cannot do online. I am always interested in the most dynamic parts of each online experience and I try to see where the limits reside. And then, if you push them a bit, you discover a lot about yourself, your friends, your 'friends', strangers, and other people.
5. To show I'm alive and active. Posting to a blog or the social web is almost like actively revealing your thoughts and internal streams of emotions. You get to see the ups and downs of a person. You get a sense of who they really are. Or at least who the really are 'online' ;]...