not sure when it was a result but wikipedia also went nofollow after spammers started using and abusing their site as well... I myself am or have already in many cases stripped out the comment function all together from my blogs because of having to moderate pain in the @$$ spammers on my blogs... Though the existing spammers I'm hunting down and shutting down and have have gotten several of their websites completely shutdown, made them lose their domain, etc. I also have a zero tolerance policy on my network and if someone even spams once or looks like they are trying to make trouble I block their IP and call their ISP and report them.
... Had another Idea mid post that I decided to do... I encrypted the form on my site so now bots can't parse my site looking to generate links and on top of that there's a captcha once the javascript is loaded. [For my url forwarding service site... similar to tunyurl.com ]
... If any one else want's here's the link to encrypt your html code free.
Code:
http://www.iwebtool.com/html_encrypter
OPEN DISCLOSURE: I have no association with above mentioned links.