Re: Is there any way to stop spammers?
http://www.bp-tricks.com/tips_and_tricks/stopping-the-sploggers/
i guess this is one of the best trick against spam blogs and “wild” registrations.
Step 1 and 2 are a bit obvious, but 3 and 4 are really efficient.
Keep in mind that on a wpmu site each blog created by a member has his first post and comment appearing on the default template – the good ol’ kakumei… on which is also written “powered by…” ( Step 2 is only for main blog i think) Spam bots eat this with delectation i suppose. 
Spam programs are written to bypass signup. Well. I presume other narrow words like join, fall in, get together are also activ in such programms. But what do these programms if you choose “groink” or “methabolic” ? So follow the explanation and choose a really original word for your signup redirection. This works well for the moment. And don’t forget to put the functions.php file the in mu-plugins folder (to be theme independant).
To use in addition with some other solutions (wp-ban, invisible defender, …) of course.
