Nouveau and 320M and screen corruption. Dithering?
There is a kernel bug (https://bugzilla.kernel.org/show_bug.cgi?id=42984) coming and going with this graphics adapter (NVidia 320M). I have it in a MacBook Air 3,2 (late 2010). In kernel 3.2 there was a corruption that was resolved in kernel 3.3. Now it is back in kernel 3.4.