Sales people tend to advocate putting the ability to “Buy Now” as in-your-face as possible. The idea is that if the customer sees a “call to action” enough, they’ll do it. I’ve been asked in various web design projects to dedicate as much as 1/4 of the page to “Buy Now!!” I’ve been instructed to add banners, animations, and even sound to push this point. The problem is, it makes users want to stab you. (Of course they can’t stab you, so they just leave.)
37signals realized that bugging users to upgrade before they even have any use for the upgrade is stupid. They now wait until they get close to maxing their account, then bug them. They realize that if you treat users like they have no value except that they might upgrade their accounts, then they won’t want to use your product. The reality is that even users that will never upgrade to a paid account are useful, since they spread the word (I am one of these customers, and look what I’m doing right now.)
I love these guys - this is the exact sort of thing that makes me want to work at a product-oriented company, not a sales-oriented one. 37signals gives away the base version of their service for free, as a demo. At one company I was once told we shouldn’t have a demo easily available because our product was too hard to set up. Wait a minute - shouldn’t we fix the product, not the website?