Gotta love looking at nofollow.net's recent changes (http://www.nonofollow.net/index.php?title=Special:Recentchanges) page and seeing how many link spammer's they have to revert out every day. Speaking as a Wiki admin, I bow before your graven image every night in praise of your having saved me from the link spam. (Well, saved me as soon as WikiMedia gets updated there).
I get some of the worries of people who decry nofollow. But there's an awful lot they're missing. It's simply the best solution anybody I know of has found, and that it actually got implemented says a lot for it as well. OTOH, it's another way for a faceless piece of software to make important decisions about what links are important and what ones aren't.
I think I'll go look into implementing it on perlmonks.org. (Another thing that should get done /before/ we get rid of the robots.txt protection.)