I think social networking site should have many different features that will make your members interested in your site. Things like sharing photos, maybe even a video upload and share options, blogs, groups, chat, forums. It should be free. I dont think that having paid services will work now. MySpace, facebook, bebo, hi5..and more..all free. Don't charge anyone! You should also have some kind of widgets integrated. Do quizzes, polls, surveys, etc. Pretty much go through myspace and see if you can have most of their features and then some new ones.
yea keep it free yet i believe it depends on what your members want to do.. for some communites all they need is a forum and profiles but others need other features... so think of what you need for your community then decide