There's something odd about the database usermeta table, primary_blog, when I added blog to users without blog.
First, a user is created at sign-up without a blog(no gimmee a blog).
When I then give a user a blog, their first/only, the primary_blog usermeta still shows blog 1. Even though the blog list(wpmu-blogs.php) shows only their new blog.
I'd enter it at trac but would like to see someone else duplicate what I see.
(Version 1.2.4 btw)