Sigh... does it consistently do this? or is it some random spike?
Even on a mac, I really don't think that it should do that. (Sorta want powermac to confirm this)
At least in my findings, it's consistent, and much more severe on less powerful systems. Just a moment ago I tested the same exact video on my single-core 2.1Ghz PowerPC G5 iMac, and processor usage wavered up and down between 70% and 85%. In cases when viewing 480p or higher video, skipping in the video playback is not uncommon because the processor is so inundated.
When not weighed down by Flash, the system can handle well-encoded 720p material just fine.
<_<
* fohfoh sniffs a "If you want to watch youtube videos, don't buy a Mac" commercial in the making.
Who says you need Flash for YouTube? I have ClickToFlash installed, which allows Safari (and other Webkit browsers) to stop flash elements from automatically loading unless clicked. In the case of YouTube, it gives you the option of playing the video with the Quicktime browser plugin instead, or even ripping it from the page and viewing it in QT player separately (comes in handy when you want more playback control).
Even without that, you can enroll in YT's HTML5 beta, which works pretty nicely. The player is written entirely in HTML5 and the video is H.264. No plugins are required for it to work... all you have to do is view it with a WebKit browser (it would work with Firefox, but they've got their panties in a bundle over using Ogg Theora over H.264).
Flash is a dying beast.
EDIT: Gah, Sstin beat me on the second half
