ok i ran green lantern quicktime hd preview full screen, while having chess, photo booth, address book, dictionary, Skype, terminal, system preferences, iTunes, app store, 3 safari tabs including this one 3 desktops with different things open, opened launchpad opened utilities all at the same time and was still watching the preview it looked like it was skipping some frames while catching but if i went back a bit to where it was buffered it was smooth.