Update: This seems to also effect id based native games and some other OpenGL applications to a point where I now login under "Fallback Mode". I can live without desktop effects but the SLI will be needed for development later on. You must specify:
nvidia-xconfig --no-composite --sli=on
Logging in under a fallback or no effects mode is required. This scenario is currently being tested with driver version 313 from fedora 18 rawhide rpmfusion repos.
This does not occur when using MATE desktop in openSUSE 12.3. Both options can be enabled and there is no performance decrease. There are currently no desktop effects enabled. The issue must be Gnome 3 related.
Nothing extracted yet.
Distributions:
Ubuntu 12.04 x86_64 with nvidia-updates - Unity 3D
Fedora 18 x86_64 with nvidia 304.40 & 313.18 - Gnome 3
Hardware:
Nvidia GeForce 8500 GT 512MB x2
16GB RAM
If composite effects are enabled when SLI is enabled then Steam Client loads slowly and will eventually respond with feedback. Mouse clicks are nearly impossible and the client has to be forcibly closed. This behavior does not occur in distributions without composite features.