On my 2006 Mac Pro, I could select 200 low-resolution quicktime movies and command them to open all at once. They would arrange themselves in diagonal rows on the screen and be ready to go within seconds. On my 2013 iMac I had to wait two or three minutes until they had all finished 'loading' and were all ready to go. Even then, the responsiveness in moving windows around was slightly laggy, and the volume control wouldn't move in any of the videos. Is this reflective of the tower vs. all-in-one, even across 7 years? Is it indicative of Mountain Lion becoming clumsier at handling these kinds of things? I don't get it. And yes, I do need adequate performance with this kind of thing, as I have thousands of old low-resolution quicktime clips that I like to sort through to rediscover gems and what not, and I like to just open them all at once and move them around and watch different ones, etc.