I'm getting the same problem since yesterday as well!!!! I have a Macbook Pro 2010 and been using it perfectly until yesterday. I updated to the latest gfxcardstatus and since then I'm starting to see this tray screen. I thought it's because of the latest version of gfxcardstatus, but I just clean installed Lion again, and the grey screen appeared in the login window. Had to restart. Seems a problem with the Intel HDm, if I force it via gfxcardstatus. Anyone help?
Btw, I'm on 10.7.4 and also upgraded to Mountain Lion GM. Same thing happens when it switches graphics.