People say that nofollow means nofollow - but I'm not so sure. I haven't conducted any conclusive studies, but I think that ALL links have value, provided that they aren't spam or anything like that.
First off, nofollow links help cover up your SEO efforts to Google, and you won't be considered suspicious.
Second, I have seen nofollow links become dofollow, so you never know.
Third, links that are nofollow can be picked up by bots and posted dofollow somewhere else - this happens constantly with Yahoo! Answers.
Fourth, I suspect that sometimes value is passed even with nofollow links.
If you get a link from Wikipedia, you better believe Google will love it - nofollow or not...
Finally, I believe that all links are followed, even if they don't pass PR or value.