Crazy but interesting - you're giving up a job that most people are getting an MBA for! Personally, I don't believe that MBA can really teach one to be an entrepreneur. Are you sure you can't just start a business without the degree? In my opinion, what you will learn in two years by doing might be far more valuable than by theory... But then, you're getting the HBS branding and network, which i hope are worth $600,000 :)