If you read as much as I do, it can be difficult to keep track of what you've already read. I've actually gotten three chapters in to a book before I realized that I'd already read it. Oops.
To help me keep track, and to keep a feel for what's coming and what's new, I use Goodreads. Think about it like a combination of Netflix and Facebook for books. With this website you are able to track books that you've read, books that you want to read, and to compare those books with your friends on the site. It's almost too easy to build up a ridiculously long to-be-read (TBR) list. Mine is 340 books long at the time I'm typing this. I'm almost embarassed by that, but then I remember that I have this blog, so in theory I'm going to be able to get to them. Honestly, I just want to read all of the books. All of them.
Once you manage to move a book off of your TBR list and actually read it, the website allows you to rate the books that you've read anywhere from 1-5 stars. The ratings are then used to create recommendations based on what you liked. Recommendations are also made based on the things you want to read. Because I need another way to get suggestions for more books to read. If I can get my read list to be longer than my TBR list I will count that as a huge accomplishment for 2013. Huge.
There are multiple groups to join, if you're interested in that sort of thing. You can add people as friends and see what they're reading. You can also compare the ratings you've given various books to what your friends thought of them.
If you're interested I highly recommend checking out the site.
You can see more about the books I've read here.