tedster - 7:37 pm on Nov 27, 2010 (gmt 0)
The worry is that websites can be penalized for linking to a bad neighborhood - and the nofollow stops that worry. No one can control what happens at the other end of a link and even though the site is fine when the link is first put in place, it takes vigilance to police your outbound dofollow links. Not every website is up to that - especially those that allow user generated content.
Still, the whole thing started with a Google penalty threat, and was designed to help sites dodge Google bullets.