I've just tried Spock yesterday and I found the concept quite interesting. Spock is a meta search engine to find... people!

Spock searches on other search engine (as Google), on community web site and on all other kind of web site to found out a person by his name or with some keywords.
As all web 2.0 new web application, you need an invite to use it!

Now, be carefull about your private information, it can be easy to find them with this tool ;)