tedster - 7:43 pm on Jan 6, 2009 (gmt 0)

The PR Update was actually a little later than that - confirmed on December 31 [webmasterworld.com] - and the update before that was in September. You probably caught the first traces of the recent toolbar update on Dec 29. That pretty much accounts for the PR changes you saw (and didn't see), and the fact that there was no impact on your traffic also lines up. TBPR changes only.