Now here's a use for social cataloging and categorizing ("folksonomies") that really interests me.
Tagging, browsing other people's lists, commenting and reviewing, are all fun themselves, but as a bonus, you get to finally catalog your own library without too much typing work.
I'm 'ijon' there. And I've only been adding sporadically so far. I'm still thinking of the sort of system I'd adopt to tackle cataloging my entire library.