I'm a fan of business plans, although like every other rational and sane person I hate writing them. One of the things that I proposed and implemented for SAP Ventures was the notion of doing a comprehensive investment memorandum to support every new investment that was proposed. It was a large document, up to 40 pages, that chronicled every aspect of the deal being proposed, and in the end it very much reflected the intentions of a business plan, to lay out all of the moving parts of the business and understand them like a working model. Sure, I hated writing these damn documents as much as everyone else on the team, but the exercise of writing them sharpened my thinking greatly.
It was surprising to me to see how many variations of the basic business plan someone could create. Typically, this exercise gets little attention in the modern startup because 1) "we're different", 2) "there's still too many holes that we need to fill, or my favorite 3) "we didn't want to put the energy into writing something that really would not be used". Too bad, writing a solid business plan is an exercise that pays out far more than you put into it, here's a proposed template. Link via Anthony.