I noticed this in Safari and iTunes first; but now I note the same thing occurs in Finder. I don't know what causes it, but it's something that "sets in" at a certain point of usage and then doesn't go away until a reboot. 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 "scrambled". While I am scrolling, large portions of the screen will also flash a neutral screen colour and rest only once I've stopped scrolling. 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?