I signed up for this site - I am not quite sure how useful it is, or if it will be another fad. I guess we will just have to wait and see what becomes of it.
You can get to the site by visiting them here: http://www.diddit.com/
Anyway - the concept is kind of interesting, you check off things you have done (basically anything) and denote things you might want to do. It is a place to share your life experiences, and discover new experiences to partake in. I guess its the newest form of social networking - trying to meet people who like to do things that you do.
I have to confess I have not actually checked off anything that I've done, but maybe I'll go do that now.
The site is currently in Alpha, so there is hopefully more to come ... but certainly check it out