Oh dear, I think I could get addicted to this.
At first, I wasn't sure what the point of Library Thing was, except as a way to compile all my favorite books into a list. For me, it was going under my profile and seeing all the users who had similar books on their lists that really changed the way I saw the site. I started with about 13 books, and then looked at my profile links and kept seeing stuff I wanted to add. Now I am at 48 books!
And I haven't even started rating them yet...
Honestly, the only thing that would keep me from being involved in this site more is time, specifically, lack of it. Otherwise, it seems really fun.
Here's a link to my library: