You like someone. They're in a relationship. Be the first to know when they're out of it. That's what it says on the Facebook Breakup Notifier site.
All you have to do is login with Facebook, choose the friends you're interested in who are taken, and get an email whenever the relationship status of your chosen friends changes. It's that easy. It's also a little creepy.
(thanks Cora)The Presurfer