Matthias Clasen on the behalf of the GNOME Release Team has announced that they have decided to eliminate GNOME’s “fallback mode” with the upcoming 3.8 release that allowed a “GNOME classic” mode that didn’t depend upon OpenGL/3D rendering and was more like the GNOME2 traitional desktop.
Now for GNOME users without a proper GPU and drivers, if you want to still use GNOME, you will need to use LLVMpipe for a software-accelerated experience of the GNOME Shell.
Gnome has totally gone off the rails. Luckily there is a fork for Gnome called Mate. Mate is supposed to be shipped with Fedora 18. I have used Mate in a Linux Mint virtual machine and it works well. I tried loading it into a Fedora 17 VM many months ago and it had problems but I’m sure all of that will get worked out. IMHO, Gnome has become a product of hubris. I’ve tried to use it and just can’t deal with the constant context switching to do simple tasks like opening a terminal window.