Recently both Dave Winer and Robert Scoble have have bemoaning the fact that the social networks out there don't allow the user to define how they want to describe a contact, nor do they let the user define the nature of the relationship with the contact, nor do they allow the user to import/export contacts from one network to the other.
I've given this a little thought (and I do mean a little thought) and the solution is pretty straight forward actually. The database schema below should allow for the above functionality, all you need to do is to wrap it in some stored procedures, wrap them in some web services and present that in a nice AJAX enabled web site and there you have a pretty good Web 2.0 business. But hey, since I don't have the financial backing to do that (plus put the server infrastructure in place) I'll leave that for someone else to do, just remember me when you become a millionaire. ;-)
Just realised this would make a great SaaS business too. Hey, anyone out there with several million quid they'd like to front me? No? Hmm, didn't think so; sigh, guess I'm just ahead of my time. :-)