I use both dofollow and nofollow in my SEO campaign. Both have value but should be used differently. Let's say I have a Facebook Fan Page with a keyword/phrase I want to rank for. There is no way that Facebook will help push my website up on the SERPs when it comes to Google juice. However, in a round about way it does! Facebook has a pagerank of 10 and is nofollow. So no juice. But if promoted correctly that Facebook Fan Page will drive traffic to your website because it will rank high in the SERPs.
It is not that hard to have a Facebook Fan Page rank well in the SERPs quickly. This means that you will have a presence on that page targeting your keywords. That presence will be reflected in more traffic. That traffic will help push your website/blog high in the SERPs.
On the other hand, you could create and develop a blog on Wordpres.com which is a dofollow and has a pagerank of 9. If you build unique and interesting content on that blog with a link to your website you will get Google Juice from that link. As with the Facebook Fan Page mentioned above it is possible for your Wordpress blog to grab one of the positions on the first page of the SERPs.
In essence, you may have 3 different properties pop up on the 1st page!
Many people do not understand how powerful blogs, Facebook, Twitter and Tumblr can be. If done correctly you can dominate the SERPs for your keyword. Note that some keywords are so competitive that it could take a long time.
In sum, both dofollow and nofollow have their own uses. Lastly you can have a dofollow pushing juice to either a nofollow or another dofollow property. One you place a nofollow into the mix the juice stops flowing from one property to another.