In my personal opinion, an incoming link is still very useful regardless of whether or not it is follow or no follow. A nofollow link from a site that matches your audience and has a reasonably good number of users is a good thing. Also I believe from an "Seo" perspective, I think no followed links help strengthen your do follow links. A natural back link profile would probably have both. In addition, it's also important to recognize that traffic is one of the main points of SEO, and no follow links can bring a lot of traffic.