What can be if every site, every directory will use just nofollow links? How it can impact Google PR? It can be in a few years. More and more sites use nofollow links.
Then i will say no more PR, and you can actually found that PR is not playing important roles in SEO world
No-follow link is also useful in search engine optimization. We should create both no-follow and do-follow back-link for our website. It helps to increase search engine ranking.
I think the most important factor is to be in the page 1 number 1 spot in Google search engine results pages.