I have made a similar proposition here and got some replies (I wasn't aware of that, but other people found it interesting too)
http://www.wwwthreads.com/perl/show...8&page=1&view=collapsed&sb=5

it's basically the same idea but I also want to let users search this information (i.e. it would be interesting to see who likes to play tennis from their profile and then see their post or send a private message. The example is not very good but I guess you see what I mean).
From what I've been told it is fairly easy to do (probably not for me unfortunately)... Have you seen the UBB? they have a mod called memberlist wich is exactly what you say. It's pretty useless (IMO) if you dont have a search posibility...

Let me know if you make something out of this