Only a few hours ago, Buffer, the web app for posting to social networking sites on a schedule, was hacked. A bunch of accounts hooked up to the service started sending out spam messages. This is always a rough position to be in. You essentially have to admit to your users that you screwed up and caused them some grief.
The blog post in question: http://open.bufferapp.com/buffer-has-been-hacked-here-is-whats-going-on/
Buffer, however, handled it particularly well.
Within an hour, they had posted on Twitter, Facebook, and their blog explaining the situation, and disabled posting on all services until they had a fix in place. They've since posted two updates and a security fix for Facebook, and are continuing to look into it. They've also said that they will respond to "every" (yes, that's quoting them) email they receive on the situation.
Now that's customer service.