I really like the reputation and collaboration pieces of this site.
What about creating a hosted service similar to
ning.com and friends? Let users create their own communities, support it with Google-style ads, etc. You'd need a place to upload files, too, and include them in wiki pages.
I participate heavily in the Yahoo! groups list for a piece of enterprise software (Epicor Vantage). If there were a viable, and better, alternative to Yahoo! groups, I'd switch.