I've had an open issue with Adobe for the past 6 weeks that was so grievous, I did not even want to talk about it openly: Flash Player 10.1 crashed to the desktop when trying to run the game Flak Cannon from "The Essential Guide To Flash Games".
I was able to zero the offending code down to the any place where there was a check of the bitmapData.hitTest(). Simply replacing that code with a standard hitTestObject() would make the problem go away...except it would also render most of the cool part of Flak Cannon useless, as the game play is pretty-much based on pixel-perfect collision detection.
I'm happy to say that Adobe informed me yesterday that this issue has been fixed in Flash Player 10.1 RC2, available here:
Whew! I'm sure this issue could have affected 100's of games and apps that have already been published on the internet. I'm very happy Adobe waited to fix bugs like this before they let 10.1 into the wild. Bravo!