@goodroi: I do actually get some referral visits from those links. I hear what you are saying about discontinuing the use of URL and it's hard to say if the amount of visits I get this way is justified or not - some of those comments require me to look something up, sometimes even try something in my lab before I post, so you can safely say many people spend less time writing some blog posts than I do posting a comment...
But I think you just made me nervous, too: I think I easily have 90%+ of links as no-follows. My own pages are scraped often (that's usually a no-follow), I have Wikipedia links - count those in nofollow camp, then those blog post comments, some forum comments, too, BTW. I guess I should have said blog and forum comments in the first place - they are very similar in every respect and of course both are usually no-follow. Social networking links (FB, Twitter) are also no-follow or redirects through URLs with unknown index-ability (almost a guarantee that they pass no PR)
I haven't specifically pursued do-follow links for this site and I have to say, I have trouble thinking of ANY type of a link that would be a guaranteed do-follow link.
Let me rephrase that: I can't think of any type of naturally acquired links these days that would be do-follow links. It is entirely possible that all 100% are no-follow. The site was started sometime in 2009 when already no one in their right mind would have linked to you without no-follow unless you paid up. I guess I can approach some of the bloggers and offer $$ for a link that's labeled "advertising" but that would be the classic paid link example that G hates so much.
So, how do you get out of this no-follow rut yet attract none of G's wrath?