Hmm. I just put together my Zacate E-350 system (ASrock E350M1), and installed 4GB of DDR3-1066, and installed Win7 64-bit, and installed the newest drivers off of Asrock.com, and that BF3 preview video played just fine full-screen.
Well, mostly. It was buffering like a b**ch, but it played back just fine. UNTIL, I double-clicked on it, to check the CPU usage, while it was buffering, and then when the video started again, this time it was unaccelerated, and the CPU went to 100%. Previously, it had hovered around 20% CPU time on both cores, for full-screen 1080P playback (1920x1200 monitor, attached by VGA).
So it looks like there are driver glitches still, but the hardware IS capable of smooth 1080P playback of flash videos.
Edit: It seems like I can't replicate this low CPU usage again. I tried watching the video in Firefox, and yes, it is around 5 FPS. Laggy, choppy, not very watchable. So I rebooted, tried IE8. Better, but still not 24FPS. I had to mess around with full-screen/windowed, and changing the resolution. I windowed, changed the resolution to 480P, full-screened, and then changed the res to 1080P. Then it played back smooth again. But when I went to check my Task Manager, it said that I was using 75-80% of the CPU. I dunno how I was using only 20% before, but perhaps that was because I was pausing and buffering all of the time.
Edit: Third time's the charm. This time, I closed all of my browsers, and opened Firefox 4.0.1, and opened a new tab with the video, and this time, I clicked full-screen FIRST, and then (after the ad had finished), I clicked on 1080P. And it played back smooth, and again it took like 20% CPU time on both cores. Sweet!
It should be noted that my first test was at 1920x1200, but the second two tests were with a monitor that is 1280x1024.