I joined Facebook to experiment with the API for a real estate and social network site. I shortly had a longish list of friends, people I'd known for years, family, coworkers, baby pictures, etc. It was fun, but it was a lot of parts of my life in one place.

Most of us live compartmental lives. We're constantly separating various aspects of our lives, cultures and relationships. People, I think, form pretty cool organic amalgamations like large cities, universities, internets, etc. But planned spaces, such as malls, airports and suburbs, tend to be insipid. Facebook is the insipid mixture, IMHO.

I don't know if all social networking sites are equally doomed, but I think it's about the next thing and not necessarily the "next best thing."