I used to have the grey screen problem too, its not Apples fault and its not the graphics card switching. Its actually caused by Flash Player 10.0 (which on Mac uses the CPU for all the processing and doesnt use the GPU at all)
To fix it, install the Flash Player 10.1 beta (the mac one is called Gala) here
http://labs.adobe.com/technologies/flashplayer10/gala/
It is very stable (for me at least) and it is the first version of Flash Player for Mac that utilises the GPU, making it much less of a system resources hog. It also eliminates the grey screen problem.
Happy Flashing