It's not quite like Blogger in that respect. Where did you here that? Your users can register themselves but the admin will have to make the blog and give the user permissions to post. If you want to hack this feature into b2evolution, then try this link:

http://plugins.b2evolution.net/index.php/2005/08/11/new_users_get_blog_immediately

Is there a clean/easy way to do this? Currently my b2evo install has 16000+ users, 16000 blogs, and 16000 categories (one for each blog). This is causing it to crash when it's trying to cache categories... because for some reason it caches all categories instead of just categories related to the current blog.

My understanding is that you can not post in a blog until you create a category in it. Is that correct?

Any help would be greatly appreciated as this is going to quickly kill my server.

Thanks,

Dan

Right, you can't post in a blog until it has a category. Once 1.6 is out, I expect someone will make a plugin that can create blogs automatically, but there's not an easy way to do it now. For your scalability issues I would suggest you talk with the developers. They would probably be interested to know about what happens with that many users.