I just made a post on my blog about Myspace and included some tips about starting your own social networking site. If you don't want to read the entire post scroll down to the last paragraph for the good stuff:
http://www.webpublishingblog.com/social-networking-the-trend-is-niche.htm
http://www.webpublishingblog.com/social-networking-the-trend-is-niche.htm