I'm running Fedora 16 64-bit, my graphics card is an Nvidia GTS 250.
Adobe flash performance is poor compared to Windows, and GPU accelerated video decoding doesn't seem to be fully working (worked in Windows).
I'm using Google Chrome, and oddly enough, flash performs (slightly) better in Firefox.
I have the Nvidia proprietary drivers installed (version 290.10), and the VDPAU and VA libraries installed.
Also, I'm running Gnome 3, and I've noticed some serious performance degradation in Gnome Shell, since switching to the proprietary drivers from Nouveau.