I like to encourage sites to sign an affiliation agreement before blindly sending them traffic (and thus vouching that I want to refer them)...
Having an option to turn off "no follow" for certain groups would be an excellent option. Right now to control spam I am just not letting new users use the sig file and in certain forums not letting them use UBB or HTML. In my case, spam tends to come mainly from the pros - and that discourages them. Once a certain post count is met the probationary period is over and full membership privileges kick in - without the "no follow" in my case as I don't really have the problem of members having sites that disappear after a few weeks or real off-topic sites being posted.
