DHH makes a few mistakes in his reasoning here. I have an MBA and work for a successful YC startup. Here are the flaws with his argument:

1. Mediocre business schools aren't worthwhile. And although school rankings are only an approximate quality measure, any school that isn't in the top 30 in the world or top 10 in the US is probably mediocre. He is basing his analysis on his experience at the University of Copenhagen, which doesn't make most global rankings (http://rankings.ft.com/businessschoolrankings/global-mba-ran..., http://online.wsj.com/public/resources/documents/MB_07_Score..., http://www.businessweek.com/bschools/rankings/), doesn't crack the top 30 in Europe (http://rankings.ft.com/businessschoolrankings/european-busin...), and doesn't actually offer an MBA (http://uk.cbs.dk/degree_programmes). In addition, the 3 year program the DHH refers to is actually an undergraduate program (the MBA is a graduate degree).

2. Internet businesses operate at large scale (if they are successful), and understanding large scale businesses operations requires quantitative analysis. Working for a YC startup myself, I can attest that what I learned in business school is incredibly useful. My school (Wharton), focused on quantitative analysis, and I came out of it with a set of tools that I use everyday. These include statistical analysis, quantitative model building, quant marketing tools, and financial analysis. Of course you can learn these tools on your own, but you risk not knowing what tools are available to address the problems you face.

3. In addition to tools, a good MBA program will teach a general problem solving technique to systematically break down, analyze, and solve business problems. And it will teach you to effectively communicate your solutions to others (you boss, a client, a VC, whoever). Some people are naturally good at this and don't need an MBA to do it. But many need to be taught how to think in this manner.

4. As another commenter pointed out, a lot of value from getting an MBA comes from networking. However if you get an MBA in one country (Denmark) and then move to another continent, that network will be less useful.

5. Many of DHH's lessons about building a successful startup - including charging for your product, picking a competitor, and rejecting conventional thinking about starting a tech company - are exactly the type of things you learn while getting an MBA. In fact, rather than learn specific lessons like these, you learn a framework for evaluating your business and market, and formulating the right way to structure your company.

DHH does make a few good points, both explicit and implied:

1. Strategy frameworks like the Porter's 5 Forces (he incorrectly describes it as a management theory) aren't particularly useful for starting companies. Although these frameworks can help to gut check if a startup is entering a good or bad market, they won't be at all useful in the day-to-day running of a company.

2. Based on my small sample set (of 1 school), I don't think business school is useful for learning how to build a product or be entrepreneurial. Granted, some schools specialize in this and mine did not, so other schools may be useful in this regard (Stanford GSB is known for entrepreneurship).