>Not sure. It seems though that you could implement a monthly or fee-per-use system quite easily without MS Passport.

Yes, but if the Web service vision is that you will interact with hundreds of Web services all of the place every day. Have 100 seperate Web service vendors bill people every month/year with pennies is not all that practical. What I believe Jim is asking, and what I have been envisioning for a while, is a global billing system what makes it easier for the consumer to handler, as opposed to more headaches.

I don't think authentification (passport) is the issue here.