On a Fedora 15 x86_64 system with all current updates, using Gnome Shell, NVIDIA driver 180.11 (and 275.19), flash plugin 64bit beta 188.8.131.52 and Google Chrome 12.0.742.124 (probably older versions as well)
Hardware: GeForce GTX 560 Ti
Flash player config :
$ cat /etc/adobe/mms.cfg
Sometimes when I try to close a tab on Google Chrome that is currently playing a youtube video (with flash player), XServer 1.10.3 freezes (>=100% CPU load) and only mouse cursor is moving.
Pausing the youtube video and closing the tab doesn't seem to trigger this problem.