Open source provides an incredible amount of technical leverage for small companies. No matter who productive your rock-star programmers are and no matter how much judo you apply to your problems, solid infrastructure takes a long time and benefits immensely from broad involvement. It really does take a village to raise great infrastructure. The Ruby on Rails framework of today is a lot more productive than the one I was using before it was open sourced. I use features every day created by others, enjoy polish done by others, evade bugs caught by others. All work I would otherwise have to do myself. So I simply get more done for less effort than it would otherwise have taken. The same holds true for the other open source projects that have been cultivated in 37signals, like Prototype and Capistrano.