I think it can be a good idea to use no follow on sitewide listings (if any). But, I am completely against using "no follow" on reviewed directory listings.
I use no-follow only on the submission page for the submission services... This is for the purpose of passing only traffic to those services.
https://www.google.com/support/webmasters/bin/answer.py?answer=35769 Make pages for users, not for search engines. "nofollow" wasn't created for users.
I have said this many times Google contradicts themselves. I think its a case of "make your site for users but also do this this and this if you want to stay in our index"
The Best reply It's time we forget what google want us to do and work on over sites and make them a useful resource. Things will follow naturally. (Like PR )