In my experience, an MBA or equivalent (meaning someone with experience building/running a business) adds value mostly through pattern recognition. In a startup, it is easy to get lost in the noise and go down many wrong paths. An MBA should be able to use their experience and knowledge to guide the company to better paths more cheaply, quickly, and efficiently. And of course, later on, grow the fledging organization (e.g. hiring, scaling the organization, etc.).

I meet and advise many entrepreneurs and most of the time they fall into common traps stemming from lack of understanding of market dynamics, how companies make decisions, what companies worry about, what matters, etc. A common example: thinking about cost and not value when it comes to selling a(n enterprise) product. Or forgetting about risk management for their new cloud-based solution.

For tech startups, there is no question that everyone on the early team needs to understand, live, and breathe technology. A lot of folks are attracted to the Facebook-size wealth generation (including MBAs) and end up destroying value because they don't understand technology.

Full disclosure: I have an MBA. I also have been programming since I was 9 and have built and sold two companies. I fully believe that a lot of MBAs don't add value when it comes to startups in particular (see Steve Blank's recent posts explaining why) and many times in mature companies as well. Of course, that is true for people in general - i.e. there are many engineers, designers, marketing folks, etc. who are just not very good at their jobs. It all comes down to looking for the exceptional gems!