While many GPUs from Nvidia, AMD, Broadcom and Intel were initially supported, some integrated solutions like the GMA 500 and GMA 950 were excluded. It's a little hard to distinguish what's new in Flash 10.1 beta 3 because it seems Adobe has merged old release notes with the latest updates (PDF). That said, the GMA 500 is now officially supported, as is the Broadcom Crystal HD accelerator found in Pine Trail-based netbooks, such as Dell's Mini 10 and HP's Mini 210.
Engadget has tried the latest build on the HP Mini 210 and it was able to cope with 720p playback on YouTube. The system didn't fare as well against 1080p video, but updated drivers might resolve that. Have you noticed a boost in performance or decreased CPU usage with Flash 10.1?