We call it CompeteMonkey.
If an users stops using foretaster, we'll receive an e-mail alert for that too! This doesn't happen that often, but if it does, it's better to find out quickly. We then send a message to the owner of the website, asking for feedback.
We've decided to monitor other services, too. Sometimes I receive an alert saying that some website deleted not only foretaster, but also other service (such as CrazyEgg in the screenshot below). And most of the time it happened by mistake.
As the name suggests, the last use case is spying on your competition. The services your competitors use can tell you a lot about their business strategy and plans!
You can start using CompeteMonkey right now. Just sign up here. It's free to use!
You can also follow CompeteMonkey on Twitter: @competemonkey