"2. Be your own customer. Try (if you can) to eat your own cooking. A product works out much better when you use it yourself. Solve your own problems. Fix the things that annoy you the most. Beyond just 37signals, there are lots of examples where people built software that succeeded in part because they use it themselves. GMail comes to mind."

This is kind of ancient wisdom in the software industry (even Microsoft does this), but as you say, it may be worth repeating.