I've nearly finished entering the data about my books into LibraryThing. Some additional thoughts I've had while cataloging:
The social data aspect of this is fascinating. I'm sure I'm not the only user who's had the experience of entering a title, seeing that nobody else has it, and then noticing weeks later that someone else has added it to their collection. It's a small but definite thrill to see that somebody else has a really obscure out-of-print book that you thought nobody else had ever heard of. It's like scoping out someone's bookshelves when you visit their house for the first time and seeing a shared book you weren't expecting to see.
This is what a commercial site like Amazon can't do: allow people to exchange recommendations and book reviews without demanding personal information.
Even with the addition of the "reviews" feature, people are using tags for very quick capsule reviews, like "lousy" or "brilliant" or "not recommended" or (my personal favorite) "thumping good read."
I wonder what percentage of users are librarians? I'm seeing a lot of people identifying themselves as librarians or MLS students in their profiles.
Patrick O'Brian fans tend to be completists. After I added my stack of Aubrey-Maturin novels to the catalog, I noticed a bunch of other people with the entire series suddenly showing up amongst my similar libraries.
I am nowhere near unselfconscious enough to tag which books I have and haven't read, like some fellow LT users are doing.
The Zeitgeist page is always interesting. J. K. Rowling has been the top author since the get-go, and The Da Vinci Code is among the top 10 books. But otherwise the holdings don't always look like the New York Times Bestseller list. Among the things that surprised me: Pride and Prejudice and Strunk and White's Elements of Style are #15 and 16 on the top books list, and The Handmaid's Tale outranks Harry Potter and the Goblet of Fire. The Odyssey comes right after David Allen's Getting Things Done in the rankings. This could be an interesting, albeit totally unscientific, way of looking at people's reading habits beyond what they've bought in the last week.
And check out the sidebar over there on the right — I've added a blog widget that displays random books from my collection.