Adobe Flash Player 10.2 was quite interesting in that it brought Linux video acceleration using NVIDIA's VDPAU API, but it didn't support Intel's VA-API. Our tests with modern NVIDIA GPUs though showed Flash Player with VDPAU works quite well, except for considering that it leaves those with open-source drivers, AMD Catalyst users with VA-API/XvBA, and Intel VA-API users in the dark without any GPU-assisted video playback.
With Flash Player 10.3, Adobe doesn't appear to yet support VA-API. Their release notes are vague as always, but grep'ing their Flash Linux library just yields VDPAU matches and nothing relating to the VA-API library (libva) or anything else. In other words, those using NVIDIA's binary driver on GeForce 8 series hardware and later have GPU video acceleration, but for everybody else, your videos are still running off the CPU. Under Windows, Adobe supports all major drivers / graphics processors.
Even the open-source Gnash Flash Player supports VA-API. We know Adobe is working on such support though, so perhaps it will come in the next beta or with Adobe Flash Player 10.4 later in the year.
The Adobe Labs mentions that this Flash Player 10.3 release implements media measurement, acoustic echo cancellation, integration with browser privacy controls for local storage, a native control panel, and auto-update notifications under Mac OS X. That's it for the official change-log.
The Flash Player 10.3 Beta can be downloaded from this Adobe Labs page.