In-service teacher training

Teachers who are already teaching benefit from additional training: what we called in-service training. Should this in-service training be internal (at school) or external (out there somewhere, like a nice fancy hotel), and how much time should be given to it? Who should conduct it? Who should be the teachers who go for this kind of training? What exactly are the benefits of it all? Today, Troy has a nerdy story about off-site in-service training from his school which gives us plenty of food for thought.