That's what makes link building such a hassle. You need to hunt for those that are followed. No follow also helps to make link building look natural. I'm currently using Alexa to look for competitors

If you are using FireFox, simple add plugin named 'NoDoFollow' and it will quickly show you whether the link is nofollow or not even without looking at the source code.

Well, I don't think you should be very concerned with it since nofollow is a PageRank issue. I've never been one of those people that only go after dofollow links.

The truth is, if the link is going to get you traffic then why wouldn't you want the link?

My advice, don't worry about it. PR isn't updated publicly and we don't know what the real PR of a site is anyway. It also doesn't mean that a nofollow link is useless for ranking purposes, that is far from the truth.

Also, save yourself some time and get the SEOquake tool bar and add the option to "strikethrough" nofollow links, that way you don't need to manually go through the source to find it.

I always think it's best to build links that actually generate traffic by providing free advice or information related to your niche. Do follow back are very good and help with your ranking, but some no follow website receive a hell of a lot of traffic.
If you create an article and included Infographics and maybe a YouTube video to engage your readers.
You could pull more traffic out of a No-follow website that ranks your content high on the search engine.