Some new social blogging sites are below - one note since the Summer is ramping up around here with vacations and trips - we'll work on bringing back the Social Thursday blog in August.
These are from the March 2007 Issue of Business 2.0.
One use for that would be to download the toolbar and then "Stumble Upon" your own site(s).
Similar to MySpace.
A way to sign into all of your IMs.
If your area of expertise doesn't have a Wiki then why not build one.