I answered a provocative question on Quora earlier this year, and thought I'd repeat the answer here:
I don't have an MBA (I have an MS in Computer Science), so I can't speak from direct experience.Does getting an MBA make someone a better entrepreneur?
As CEO, I've managed dozens of MBAs in my career, so this answer is based on that experience. An MBA provides a fair amount of knowledge about historical business case studies, finance, and other topics -- all of which can be useful. It is in no way a substitute for real management experience and that's where it can be harmful -- when the holder of the MBA thinks they know how to manage, because they have an MBA.
If you think of management as a systems problem where your task is to design and maintain a system where it's a) easy to get meaningful work done and b) is fun to work in and c) you will be recognized for your good work, then the relevant experiences for management are to a) work in a company and find out why it's hard to get things done or b) run a company and carefully observe how you are screwing it up.
If you think that you know what you are doing without these experiences, you are likely delusional and would have been better off just drinking beer rather than getting an MBA and drinking beer.