I use aNobii to keep track of the books that I own or have read from the library. You can see the recent ones over on the sidebar. Besides having a nice interface, you can add lots of metadata to each book to keep track of whether or not you finished it, if you got it from the library or the bookstore that you bought it from. It will show you how many pages you’ve read each year.
Google just added a My Library feature to their awesome books project. It’s nice because it’s extremely snappy and, well, it’s made by Google. But you can’t do lots of basic things that aNobii and other online libraries like Shelfari and LibraryThing have. But once they get there, their integration within finding books at the library and viewing snippets online will be awesome.