I remember HH the Dalai Lama mentioning once that in his own culture, they don't have a word for "guilt" as other cultures do. They have a word for regret, for the feeling you get when you look back on something you did and decide that another choice would have been better. However, that's not the same as beating oneself up. I would say that regret is useful. Guilt... can be, but it can also get really masturbatory. It's easy to spend so much time beating ourselves up that we miss an opportunity to actually repair what we did, or learn how to do better in the future. If we do that, what have we really shown our priority is?