Since people have been mentioning it, but not directly:
youtube.com/html5
Safari 4.04 running on a 2006 C2D Macbook-10.6.2 with 10 tabs open and clickToflash enabled (so there's no ads or crap running in the background) uses 9% to 14% of the CPU cycles. If I go to youtube and watch a video in flash, the flash plugin adds another 33% to 50%, percent to the processor load, plus safari uses at least an additional 10%. If I use the HTML 5 option for the same video, safari's cpu cycles go up about 15%, and there's no flash plugin running.. (tried to average between 6 different videos, your mileage may vary)
Flash has always been a second class citizen on the mac platform, hell almost 3rd class.. Adobe hasn't done anything to remedy the situation. They obviously have put more work in on the windows plugin.
I can go both ways with flash support on the iPad, there's definitely more of a reason to have it than on iPhone/iPod Touch. Even if they did add it, I'd want ClickToFlash on to stop all the crap flash ads from popping up .
As it stands right now I could do 95% of what I use this laptop for on an iPad, that remaining 5% would be watching embedded flash videos, and maybe using CSSEdit, and BBEdit.. If I'm doing any sort of image editing page layout or video editing I do that on my desktop, and that sort of thing I'll always do on my desktop.
If Adobe actually put some time in on the Arm based flash plugin, and it was efficient, and Apple added ClickToFlash to mobile Safari, I'd say we'd have the best of both worlds..
I'm not counting on it though..