A new service, called Qwitter, has debuted today, allowing users to find out when others stop following them on Twitter. From time to time, you are going to lose followers, whether it be because you have said something that your followers don't agree with, or because they no longer find your tweets relevant or interesting. Services like Facebook and Twitter intentionally don't expose the data for when someone de-friends or un-follows you because it can potentially be a sensitive issue. Qwitter is trying to tap into the "too curious for their own good" market.
After signing up for the service, when someone stops following you on Twitter, you will receive an email stating who stopped following and after which tweet. Qwitter's site gives the following example.
John Gruber (gruber) stopped following you on Twitter after you posted this tweet:
What's the difference between Arial and Helvetica?
Qwitter might satisfy some people's curiosity, but the knowledge that the person was not going to find out when you stop following them has been wiped away. You now have to be more conscious of your un-following habits.