Kind of like a Last.fm for video, Trakt tracks what TV shows and movies you watch, digests the data, and suggests other TV shows and movies you might enjoy. Better yet, you can get plug-ins for your media centre so you don't have to bother feeding it the information manually.
Trakt is really easy to use. You just sign up and start liking (and disliking) TV shows and movies. That's all you really need to do to start getting recommendations. If you want to see what other people are watching, you can pay attention to the popular charts to discover what's high on the lists of other users. You can really make the best use of Trakt by installing one of their plugins into your media centre. Currently XBMC, MediaPortal, Plex and Boxee are supported — and we've seen how simple it is to install plug-ins in XBMC, at least. These plugins completely automate the process of reporting what you're watching and keeping that up to date.