I'm surprised to see most answers are very negative. I am not sure that paying for an MBA is worth the money, but if you take out the money aspect, I'd say there is no reason why having a MBA should be anything but positive...
I think:
1. there is a tough selection process to get in, so chances that if you get an MBA from Harvard, you're a pretty smart person
2. MBA classes should give you valuable lessons, that you won't get from Startup School or YC.