I've been searching like mad, but haven't been able to find anyone with a similar problem, so here it goes.
I'm running Ubuntu 12.10 with GNOME 3 on my Lenovo T400. Almost once every day or two, I'll have a couple windows open, and all of a sudden, they'll disappear. The only thing that's left is my background with the top panel from GNOME. (And I think it's grayed out a bit, like something's overlaid on the backgroud.)
If I hit the Windows super key or click "Activities", they'll all show up, as usual. However, the favorites menu along with the search bar will be missing. As soon as I hit the super key to return, the windows disappear again, leaving me with only the desktop. Similarly, Alt+Tab brings shows me the different windows (as I have Coverflow installed), but then nothing once I let go.
Any similar problems, suggestions, references?