There's a database of books I can browse or search through and rate on a scale of one to five stars. So far I've made it through 229 of all the books I've ever read. How did I have time? Rafe Needleman asked me to write this blog posting, and therefore it became "work."
You can also add books to shelves. The default is to add it to a "read" shelf but I also added the books I'm currently reading to the "currently reading" shelf. And I even added a book to the "to-read" shelf.
On any given book you can write a review to support your rating, a little like how it works at Amazon.com. I didn't do that to the 229 books I rated.
I'll have to give it a little time to see if I really use it as a recommendation engine or not. In the meantime, it was fun to browse through and remember books I'd read but hadn't thought about in a long time.