I noticed this in Safari and iTunes. I don't know what causes it, but it only happens occasionally. In Safari, when scrolling up and down webpages, the alignment of the page becomes corrupted. So, for example, scrolling down the forum board on Macrumours causes the individual forums to come out of alignment and become distorted. Small squarish parts of the screen also flash a neutral screen colour as I scroll up and down. Same thing happens in iTunes. In grid view, scrolling up and down my library causes a fairly large portion of the window to "black out" or flash for short instants before revealing the content again. Anybody know what's up?