I've had a few friends report strange issues with their MacBook Pro laptops. Often they would report that the video signal on either an internal or external display becomes 'glitchy' or 'jumpy'. I initially thought it could be a connection issue, as I've seen many a VGA cable that becomes loose cause weird sync issues. However, they also reported that the cursor continued to work normally, moving around when they were moving the mouse/trackpad.
Doesn't look too nice...
I typically recommend people take these sorts of issues to the Genius Bar at an Apple Store, especially since the problem isn't easy to replicate when I take a minute or two to look at the laptop—often the problem only happens after constantly using the computer for more than half an hour.
However, I finally got to experience the problem first-hand, when my sister brought me her laptop and I used it for an evening of blogging and browsing. After half an hour or so, the screen started getting quite jittery (click through to view video and read more):