I have used friendster and orkut since the early days, sort of waiting for them to come up with features that would actually make them useful for *something*.
Five years later and after adding myspace and facebook because friends told me they were "much better" I am still basically waiting for anyone to develop a killer app that would actually take advantage of people's established networks for something useful. Something... anything. I'm still waiting, and really not using these sites for anything anymore.
The only ones I find useful are LinkedIn and
last.fm, which as a big music fan I find fantastic.