The release notes for the Flash Player 11.2 Beta state, "This release includes new features as well as enhancements and bug fixes related to security, stability, performance, and device compatibility."
The release features for version 11.2 is multi-threaded video decoding and Flash Player background updates. However, only the former is supported under Linux. "he video decoding pipeline is now fully multi-threaded. This featureshould improve the overall performance on all platforms. Note that this feature is a significant architecture change required for other future improvements."
The Adobe release notes go on to share, "Multi-threaded pipeline was written grounds up to support lower end devices and full hardware stacks where all the decoding and rendering is offloaded to hardware. The benefits of the modernization of the pipeline would be visible from mobile devices, tvs, netbooks to high end desktops. In Flash Player 11.2, the new video pipeline is available for desktop platforms (including netbooks)."
In poking through the libflashplayer.so binary file for Flash 11.2 on Linux, it appears that NVIDIA VDPAU and Broadcom Crystal HD remain the only supported GPU-based video decode mechanisms. There still isn't any XvBA (AMD's Linux video API for their UVD2 engine with the proprietary Catalyst driver) or VA-API (the other leading Linux video acceleration API) are yet supported by the Adobe Flash Player.
Flash Player 11.2 for Linux (and Windows and Mac OS X) in 32-bit and 64-bit flavors can be downloaded from Adobe Labs. From there are also the release notes in PDF form.
Flash Player 11 previously introduced proper 64-bit support, stability and performance improvements, and the new Stage 3D APIs, among other new features.