I recently changed over from ReadyDLNA to Plex, largely for the remote access that is handled very nicely by Plex Media Server (and was tricky doing port forwarding on my home network on ReadyDLNA), and my kids have quickly adapted to this as the easiest way to watch a movie... hand Dad the new disc, and ask very patiently when Plex will have it up so they can watch. Yes, I have replaced enough DVD/BR discs that I decided enough was enough.
Anyway, while my FreeNAS (FreeBSD OS) box is currently on an Athlon 5350 APU, I'm seeing that while the 2.05Ghz*4 CPU base is far more than sufficient to stream HD to 2 or 3 clients, I am not seeing ANY activity on the embedded R3 GPU. The driver base is loaded and the GPU is recognized as a processor, but Plex MS doesn't seem to use the GPU in any way on FreeBSD... and I may be wrong, but I can't find any reference on other operating systems including GPU acceleration.
By speeds, the wimpy R3 GPU should still be able to decode and recode 5-6 sessions (based on my H.264 encoding method) without needing the CPU at all. I would very much like to see GPU acceleration in Plex as it would reduce CPU strain on low-temp low-power units like mine.