I think the reason is all the things you mentioned, and more. Most of the other project management software still seems sterile, and you have no sense of who i

I think the reason is all the things you mentioned, and more. Most of the other project management software still seems sterile, and you have no sense of who is creating it. As far as features go, if everyone on a team isn't using a feature, that feature doesn't exist anyway. With the high profile of 37signals team, you get a sense that if anything was drastically wrong with the software, the user base will be able to hunt down Jason Fried and get the thing working again. If they're not gonna fix it, Jason Fried will be the first person to say so. Thats straightforward, and people use straightforward as a proxy for 'good.'