I want to start by saying that there is a lot to Shelfari. It provides ways to organize your books as well as detailed, user submitted information about each book. Some of the books do not have complete information, but it's easy to edit any book's page and editors are even ranked, so that you have a sense of accomplishment when you contribute. You can choose what cover displays on your bookself, include when you finished a book, rate the book, and other things.
Shelfari also contains a few other features. One of them is groups-pretty self explanatory, ways to connect with other users. Another feature is recommendations. Recommendations are a great idea in theory, but unfortunately they don't seem to have much of an algorithm going on. They make simple recommendations at best. Still, better than nothing. Shelfari also has the ability to ask and answer questions about a book. This has the potential to be useful, though most of the questions I saw were just of the "Should I read this book" variety. If you've ever tried to answer such a question before, you know it's not an easy task.
The last feature I want to discuss is reading stats. This has to be my favorite thing, simply because I love numbers. If you visit your personal reading stats page you can see all sorts of fun information, such as how you usually rate books, the subjects you read, and the page count of the books you've read.
Shelfari is definitely complex, and it can be a little hard to figure out at first. However, if you're looking for a way to organize all the books you've read, then it is definitely worth checking out.
Do you use an online tool to organize what you've read? What is it? Have you used Shelfari? Let me know!