Multi-DB Questions

Howdy,

I have some questions on Multi-DB plug-in. Here goes :

1) Does Edublogs, WP.com and other popular MU sites use Multi-DB?

2) Upto how many blogs can a normal WPMU installation handle and how many can Multi-DB handle?

3) What could possibly happen if I continue with my normal WPMU installation and I get a huge number of users like Edublogs or WP.com?