Good news for every nVidia user using the nVidia proprietary driver : most of the problems we had on GeForce 7 and 8 with nVidia proprietary driver seem to have been fixed in the latest nVidia driver release.
It's the release 177.67.
They are still marked as beta, but I think they're worth switching to them.
x86 64 bits : http://www.nvidia.com/object/linux_display_amd64_177.67.html
x86 32 bits : http://www.nvidia.com/object/linux_display_ia32_177.67.html
So every one suffering problems with 2D acceleration problems with nVidia proprietary driver should upgrade as soon as possible...