Library Thing (Revisited)
Rick Brannan, Brandon Wason, Bryan Cox, and I have joined Library Thing, an online service for cataloging personal book collections. It doesn't require any software, and it's free up to 200 books. (For a lifetime fee of $10 you can catalog any number of books.) It's really nifty, allowing you to visit other people's libraries, and links you immediately to those who share your interests.
I only started cataloging yesterday, prodded by Rick's recent blogpost, and am over 80 books -- I'll end up going way over 200, of course. This is what my catalog looks like so far. I agree with Brandon: it would be nice to see more bibliobloggers join.