WordPress MU

I know I am going to get a bunch of laughs on this one, but please help me out:

If I have just one blog, and 1,000 users, I am only using 10 tables, correct?

If I have 10 blogs, and 10,000 with access to all of the blogs ( I guess on a publisher level ), I am only using 100 tables?

Or is it every time I register a user a table(s) is added?

Tables are added just for blogs.
http://codex.wordpress.org/WPMU_Database_Description

at then end of the day, you're still going to have a ton of data for all those users.