conor - 9:48 am on Aug 4, 2010 (gmt 0)
Google has stated previously that almost all of PR is Transfered by 301 but not all. Whether this percentage has changed after Mayday I cant comment.
Internal linking to 301 urls has never been a best practice - where we have caught and rectified this we have always seem benefit
We did see ranking improvements after we applied the canonical tag, but there was a 2 month lag. As other changes were being made it is hard to attribute the benefit directly but I am convinced it helped.