I have an iMac 24 from 2009 and an iMac 27 from early 2011 with i5, both running O.S.10.6.8 as I have zero wish to use Lion now or in the future... The 24 has the 640 gb hard disk and the 27 the 1TB. I usually put the machines into sleep mode at night but have been surprised to find that whereas the 24 remains stone cold while in sleep that the 27 can run quite warm in the same function. Checking the Activity Monitor on the 27 after awakening from sleep,I see that the CPU is busy - I do have a large iTunes library with many films I watch via Apple TV, and I note that Quick Time takes up most of my usage, presumably down to this ? Is it better to close down applications like iTunes, Vuze, Skype and Firefox before I put the machine into sleep mode - and also to keep your iTunes Library small and just store movies on an external hard drive (as I do anyway..) and load them when you intend to watch ? Any thoughts welcomed.