I told my manager I'm leaving because I'm on really good terms with him. I am also going to use him as a reference for any jobs I apply to, so it works out well. He knows that I'm underpaid and getting screwed so he says "You gotta do what you gotta do, and I am cool with that."
But yea, I say fsck them and look for another job. I wouldn't mention it to anybody at work though.