Flash 10.1 GPU acceleration (non-scientific) tested. WHQL drivers make a difference.

MBpro, dual core 2.4 Ghz, Nvidia 8600M GT, bootcamp Win 7

2012 trailer in HD:
http://www.youtube.com/watch?v=Hz86TsGx3fc

[Default bootcamp/Win 7 drivers]

Using Flash 10.0.32.18, bootcamp/Win drivers, CPU usage averaged around 55%:

Using Flash 10.1.51.25 beta, bootcamp/Win drivers, CPU usage averaged around 65%:

[Updated default bootcamp/Win 7 drivers to Nvidia's latest 186.81 WHQL drivers]

Using Flash 10.0.32.18, 186.81 WHQL drivers, CPU usage averaged around 50%:

Using Flash 10.1.51.25 beta, 186.81 WHQL drivers, CPU usage averaged around 35%:

Summary:
Using the default drivers I didn't notice a big difference when upgrading to the Flash beta (55% to 50%) .  When I switched drivers to 186.81 I saw a decrease in CPU usage from ~65% to ~35%. wow

[UPDATE]  It looks like AnandTech came up with similar numbers, from 450% to 190%.  CPU usage dropped by more than half.
http://www.anandtech.com/video/showdoc.aspx?i=3678&p=5