Comment 7 for bug 899669

I have been having a very similar issue with Ubuntu 12.10 and Gnome Shell. I am not entirely sure but I think that I have now fixed it by replacing my video card. The old one was an ATI X1300 with 128 megs and the new one is an ATI HD4650 with 512 megs. I suspect that the old card was only marginally able to keep up with the systems's demands while the new one has no issue. Meanwhile, you can do an ALT-F2 and then type r and return to restart the Gnome Shell. Until I was able to replace my video board that worked for me every time. Hope that helps.