Lee Odden has released a list of things that he dislikes about blogs and you would rather check this out and make sure you are not doing these mistakes on your blog.
Personally I am enjoying rewarding people who comment on my blog by disabling the ‘Nofollow’ tag.
Glad you liked the list. I suppose I could test comments without nofollow, but I already get 10 or more manual email spams a day and twice that many that get put into moderation from our spam filter. 90% of those are spam.
Lee
As you see, you are getting spam comments even when you do not have “Nofollow” turned off. Spammers will bother you anyway but why make the nice contributors miss out?