Always know the next unwatched episode of each show you're tracking.
Sync your watch lists across devices using Google or Dropbox.
Have each episode you've watched be added to your Facebook timeline using Facebook OpenGraph. It won't clutter your friends news feeds unless they're interested in the same thing.
It's a one-page app using HTML/JS using REST APIs to a J2EE backend hosted on Google App Engine.
The project is available on Github so why not contribute?