One way to stop spam blog signups is to ban their email address. This can be done in the Site Admin -> Options menu. Scroll down until you find the “Ban email registrations” box. Now if you’ve run a WPMU setup for any length of time, you may already have noticed that once you put a domain in that field, like spamsite1.info, another two or twenty show up to the party.
Initially in my testing, placing *.info didn’t work. So I filed a trac ticket, and Donncha kinda explained the correct usage. To use, place /.*\.info/ in there to block ALL signups from ANY domain ending in .info.
Please remember to use with care, so you don’t accidentally block potential users. 
(Like anyone with a .com address, for instance.)
may already have noticed that once you put a domain in that field
Banning .info s would take them all out. There are some legit ones out there as well though i agree. info’s are the spammers favorite.
Spam does seem to be getting worse and worse these days. I agree that .infos are a spammer favourite but I know that there are many legit .info sites out there. Akismet works ok for my blog.
Thanks for tip. Is there a downside to using Akismet or other spam blocker as opposed to using the wildcard method?
This seems to be broken in 3.0, seems like it filters out anything other than something@something.tld
Don’t include the something@. It bans email addresses from the domains you enter not email addresses that you enter.