I've noticed that the new sophisticated video codecs really do like dual core CPUs. Before this January I was using an Intel 3.73ghz single core cpu - the fastest single core they ever made. And I could not play back 1080p Quicktime movie trailers at all well - whever it got to an action packed scene (higher bitrates) the CPU would max out at 100% and video would stutter badly. 720p was OK. I suspect HD-DVD and Blu-ray playback would have been pathetic.

Now I'm using an Intel quad core @ 2.93ghz and the system loafs playing the very same 1080p Quicktime files I've never seen more than 27% CPU utilization during the most complex scenes.

Oh, and with the Core CPUs you could probably get away with 1.83ghz...