Do the guys and gals at Google ever stop innovating? One of the latest things to come out is Google's Friend Connect. This service basically will be able to turn any website into a "facebook" type site. Through these google apps, people will be able to interact with each other when they are logged into your site. They will also be able to leave comments throughout a string of networks. It will be a way to allow friends of friends to interact with comments throughout many sites.
For some examples check out the friend connect website. Or head over to BibleApps.com.
I'll try to share more when I get some time to test this out on one of my sites.