Seems to make sense to me that any link on the internet going back to your site is a good link nofollow or dofollow.
i have made only one comment on a nofollow blog post which related to my blog page niche, and then the pr of my blog page get 1 .
Sure, NF sites can give traffic...but I am after organic traffic - in other words, I only care about ranking high in the SERP's. Basically, my backlink campaign consists of links from "on-topic" sites that are relevant to my site - and they are all "DF" sites. I've seen my sites rise in competitve niches - so, as for me - putting links on doFollow sites are really helping me. I really don't waste my time w/ NF sites.