Many people think it's very cool to sign up 10 blogs and add random garbage, or something else cut'n'paste, and that's it.
I have a sitewide RSS feed and I use that to review new entries, and I've used to nuke spam-blogs on sight. I have also use a CAPTCHA to sign up new blogs, which does help - but it doesn't help against manual spammers, and there's plenty of those.
Now I've changd strategy.
Now I Change Password and E-mail of the Spamblog-users. Then I change the spammed links to my sites. Then I'm done.
This seems to make spammers immensily angry, since they have to do all the "hard work" of making the spam-blog, cutting'and'pasting in bullshit text, and I get the actual SEO effect. This actually seems to piss spammers off enough to stop spamming my site.
It works. For me. For now. I don't know how effective it'll be in the long run, but it's a tip. For now.
Also, use the CAPTCHA for comments in blogs. People manually sign up for spam-blogs, but I've actually NEVER seen comment spam since I started using the comment CATPCHA sitewide. People seem to bother to sign up spam-blogs, but nobody bothers manual commentspamming.