There are several reports that say that there are serious performance issues using 12.04 and nVidia 7100.
Are there any work-a-round in sight?
This is how I solved the problem (found in a discussion in ubuntuforum.org). I installed the old nvidia-173 driver AND downgraded xserver-xorg. After this XBMC, Unity and other GPU-hungry things started to work again.
1) /etc/apt/preferences.d/10xorg
Package: xorg xserver-xorg*
Pin: release a=oneiric
Pin-Priority: 1050
# So i can find dependencies for the older driver
2) /etc/X11/xorg.conf
# New section
Section "Extensions"
Option "Composite" "Disable"
EndSection
3) install nvidia-173 using synaptic or apt-get
