The most important issue is whether or not users can do what they want. Build an experience, not a site. Don't try to imitate life. Use the aspects of the web to make an experience better than life. Chat is ephemeral, quickly degrading into flames and flirting.
Community requires identity, either persistent user names or self-adminisered profiles.
A good site is both learnable and intutitve. Nielsen Study of trust in communities Jakob Nielsen Nathan Shedroff Party time. Design gurus Jakob Nielsen and Donald Norman debuted their Siskel and Ebert routine. The Wall Street Journal is not a bad model for a web site. Easy to find things.