Brad's already pledged support for
Google's new initiative for preventing comment spam, but I thought I'd bring it to all of your attention.
Also, it occurs to me that the attribute might be useful to prevent userinfo spamming: if you put rel='nofollow' on all of my friendofs, then my userinfo page isn't giving them credit. (If they are my friends and deserve credit, I'll link to them as friends anyway.)
(I'm not speaking for my employer, just a friendly thought.)