Google blogoscoped has put together a very interesting list of how Google makes money from paid members, Adwords and Affiliate links on its many different websites. What is most fascinating is the large number of sites that uses neither.
It would be very interesting to get an understanding of the processes at Google when they decide which products and services to charge for and what business models to use. Given that they have so many different services, value propositions and business models, and the fact that users of free services build loyalty to and also visit other paid for or ad-financed websites, makes it very complex. No company in the world can have so much user data as Google, knowing exactly how one service builds traffic for another and what the habits of its users are. If anyone knows more about this please let me know.
Loyal and happy users is a very strong control mechanism and providing many of its services for free without any advertising Google is surely making users happy.