According to TechCrunch, Breakup Notifier was shutdown by Facebook today. The app had collected 3.6 million users in the 2ish days it was active.
Original Post 2/21/11:
Find Out How Many People Use 1,000 of Your Favorite Social Networks, Apps and Digital Services
The app is simple- Sign in to the app using your Facebook log in; Choose which friends you would like to monitor and receive an email whenever their relationship status changes.
There you have it. Good Luck?