We’ve had some reports that Qwitter hasn’t been as reliable lately as it had been in the past. An alternative service that also notifies you when you lose a follower  is http://twitterless.com/. If you really want to keep on top of when your followers jump ship, it might be a good idea to sign up for both services to make sure you have all your bases covered.

"Whats Qwitter"
Once you’ve done your initial cleaning, Qwitter is a nice app that will update you via email whenever someone stops following you. It will even let you know what you tweeted that caused them to stop following you, which could be useful (if you lose five followers every time you tweet about your cat, for example, that might be a hint to stop talking so much about your cat if you want to retain followers).