Well, I am going to provide a very subjective opinion here, but would love to get some responses...
Most top ranked MBA programs cater to those who want to do one of 4 things after they graduate:
1. Become an Associate/VP in Private Equity 2. Become an Associate/VP in a Hedge Fund/Trading 3. Become an Associate in Management Consulting 4. Become a corporate executive
Now an MBA has some real benefit for those entering these fields and there is nothing wrong there. If you're an entrepreneur, I don't really see the added benefit of getting an MBA. Most of the knowledge obtained in the coursework can be learned through experience or just by picking up some literature (see "The 10-day MBA" by Steven Silbiger). From many seasoned entrepreneurs I've spoken with, an MBA limits the time you could be spending starting your business (unless you can start while in your program like Jerry Yang or Sergey/Larry)
There is an advantage through networking with other like-minded entrepreneurs in your program and using the school's resources, but it pretty much stops there.
The one exception I would make for an MBA program really benefiting the entrepreneur is hands down...Stanford.
Stanford has the proximity to the Valley and also the roster of success stories (yahoo, google, HP, Cisco, Sun) but it's real value is that it serves as an ad-hoc incubator for start-up innovation. Just take a minute and subscribe to the free podcasts from the STVP (Stanford Technology Ventures Program) on itunes and you'll get an idea of why Stanford seems to be the only program that values entrepreneurship.
If anyone can think of other MBA programs that help entrepreneurs, I would like to hear about them.