A few more sites that help to find co-founders:

http://founderdating.com/ http://startupsquare.com/

Why don't you start a meetup group like this one? http://www.meetup.com/Co-Founders-Wanted-Meetup/ Briefings from the meetings: http://aurametrix.blogspot.com/2010/03/bay-area-startups-loo... http://aurametrix.blogspot.com/2009/11/bay-area-startups-loo...

If you want to build something similar to what already exists, you will be able to do it by yourself. If you want to create something like e-Harmony - matching people based on demographic, educational, job history, psychological and behavioral characteristics and their encounters, feeding gigabytes of data into sophisticated models on a daily basis, think about measurable expectations before proceeding.