This is sounding very strange to me indeed! 37Signals is very much known for creating the simplest of interfaces and I really found people finding it very intuitive. But this is strange… now they are asking people to buy a book for $10 to learn how to use Basecamp! Can you believe it? See the sales post (!) here at “Sams Teach Yourself Basecamp in 10 Minutes” is a comprehensive guide to Basecamp
They claim to have 3 million users on Basecamp. I think $20K is not something that makes them any richer!
In fact I would think it gives a wrong signal, like you need to learn by reading a book to use Basecamp, what people seem to know anyways!