Here's an article about the Google mail service:
http://www.computerworld.com/softwaretopics/software/groupware/story/0,10801,91814,00.html
Here's a part that should scare privacy advocates:
> One way Google will pay for the provisioning of the 1GB of storage per
> user will be by selling advertisements that appear next to e-mail messages
> and are keyed to the content of each message
Francoise