I used skitch to notify bug on projet I work on ! Actually all the printscreen are over the similar directory, so it's all mixed and hard to find printscreen from a dedicated project.
I recently used Skitch to critique a website, it worked great, but then I had to email the developer 20+ links. I wish I could have just grouped all those screen shots together and sent him that group. It was a real time sink, and getting his feedback will be a bit clunky too.