Transforming Google into a Free Online Dating Service and Social Networking Community
Why build the mesh when you can add a layer on top of an existing one? SocialGrid defines itself as a social networking community/online dating service that uses Google to hook people up. You place a unique identification string on your personal page/weblog and others find you through search codes based on common interests.
I see a dating service, closer in some ways to the GeoTags concept rather than an actual social network (even if it does plug your existing network affiliations on your profile page), but the concept is interesting.