Somethin that those of us not using the invite only mecahnism to get people started using WPMU (i.e. http://edublogs.org) would be keen to see developed is some sort of way to combat spam blogs being created on their site.
I haven't had this myself but it's probably just a matter of time... I guess there are two main issues to deal with:
-automated registraion (captcha or a rego moderation option might work here?)
-registration by human, use as spam (which I guess is a Blogger trait) where I figure using existing WP plugins to identify posting by machine as opposed to posting by human?
Not a great problem if you've got, say, 100 blogs... but we've got 787 at the moment and growing (in about a month!)
What do other people think?
Cheers, James