Guy Kawasaki mentions a study on companies starting with formal business plans and found “no statistical difference in success between those businesses started with formal written plans and those without them...”
BDUF doesn't seem too important for the suits, either.
Guy has a nice balancing comment:
However, don't draw the wrong conclusion from this study: “Analysis, planning, vision, and communication are unnecessary.” This isn't true. What is true is that a business plan should not take on a life of its own. It is a tool—one of many that may help you get funded (or, more accurately, hinder you from getting funded if you don't have one) and may help you get your team working as a team. But it is not an end in itself.