aristotle - 11:57 pm on May 8, 2010 (gmt 0)
I work with one site that has historically received a lot of off-theme long tail traffic - pretty much an accidental match based on high PR. That traffic never really wanted our page and most of the visits were bounces. That traffic has now vanished.
This suggests that in the Google algorithm the weighting of relevance has increased whereas PR now has less weight. Of course this is just one case, so doesn't lead to a general conclusion. But it's interesting nevertheless..