PR Sculpting and Link Juice and No-Follow – Oh My We made a video at SMX Advanced with Stephen Spencer recently where we discussed (among other things) some changes expected(?) to be coming to Google in terms of the no-follow attribute. These no-follow changes have some pretty significant implications for lots of things, first and foremost though it seems these changes are specifically geared to mitigate, to some degree, the effectiveness of PR sculpting.
http://www.webpronews.com/topnews/2009/06/09/google-changes-to-no-follow-on-the-horizon