Just out of curiosity, why do you use 37 Signal products? I think their "Getting Real" manifesto is solid, but don't understand why people pay a monthly subscription when there are better and free options available e.g. Google Docs. Is it just the skinabilty so it looks like you have your own site or is there something I'm missing?
Google docs is good for some things, particularly working collaboratively on docs - but fall short on things like shared messages and to-do lists. Basecamp is just so easy, and the price is so low for a business that it is worth the 40$ a month.