WordPress MU

I'm wondering if when a user registers with WP MU, do they become registered with all blogs on that installation?

Or is it on a per blog basis?

I want to have like 10 different blogs and when a user registers with the overall site, they are able to comment on any of the blogs, etc.

Is that the way it works or is there a way to do this? New to WPMU.

Thanks!

If a user is registered on MU just as a user, then if the sub-blogs have "must be registered and logged in to comment" then yes, they can comment. But they will not be listed as subscribers to each blog.

There's this wonderful plugin, but it requires buddypress installed.

http://code.ourcommoninterest.org/2009/01/02/community-and-group-blogs-in-a-can/

"Firefox can't find the server at code.ourcommoninterest.org."

Wildcard subdomains aren't set up.