social networking site open source code???

Nice. I think the pieces are there, many of them:

http://www.sourceforge.net/projects/grabthemic
http://www.missingmethod.com/2007/01/08/how-to-build-a-social-network-with-ruby-on-rails/

phpizabi.net is a php myspace clone and is pretty popular, you might
want to give it a try.

I will definitely check out the rails grabthemic sometime soon!

Andy