I believe this is a known bug with player 10 on the Mac
Sure, I'm not claiming it's not a bug. If anything it's almost criminally negligent programming . You have to go out of your way to write software that is so poor.
But let's put this in different perspective. Because CPU usage spikes so much when flash is used, even on Core 2 Duo CPUs the power usage is going to go up 40 Watts. On Mac Pro, this is even higher. But let's go with the lower figure.
Let's also assume that an average Mac user watches an hour of you tube video a day. A fairly conservative estimate I would imagine. That translates into 1.24 giga Watts of wasted energy (assuming 40 million Mac users, again conservative. Apple claims there are 70 million). That's more than enough power to supply 1000 American households in that same month. All gone wasted because a programmer sitting in a cube somewhere doesn't know what they are doing. If you think I'm harsh, don't. I make my living by writing software too.
I do agree. Though, to be fair, people use the software that Adobe creates to create their own software that runs in the flash player. The player can be as well written as it is possible to be, and still have this type of problem if independent developers write poor software. This is not in Adobe's control.
My note is that it is a known bug for player 10 to be excessively wasteful on the Mac platform, regardless of how well the program running is programmed. This is a bug that they are currently working on fixing, to all publicly facing knowledge.
The only way to truly get rid of this is to get the developers out there in the world educated in good programming habits. Actionscript 3 has done a lot in terms of pushing the community towards that goal, but bad practices are still extant. People don't remove event listeners when they are finished with them. People don't set variables to null for garbage collection. Both of these are probably the biggest problems, leaving things in memory that you aren't even using anymore. And there is nothing Adobe can do about it except attempt to educate the masses.
This is a well-known issue with the Flash/Shockwave browser plugins and is not unique to OSX (occurs on Windows as well). It will cause problems even when there is no Flash on the page. It's most likely an implementation problem with polling on Adobe's side. Uninstalling Flash+Shockwave player fixes the issue.
Firefox thread documenting behavior: