Based on customer feedback, I've made a change to the CPU Heuristic that might be of use.
The changed is the a configuration parameter that sets a minimum bitrate for the CPU Heuristic to consider suspending. I've set a default minimum bitrate of one megabit per second.
Eric Juteau suggested something along these lines -- observing that on PC's with low performance video cards they often get as limited by "StretchBLT"ing the video onto the display as much as they might tax the CPU by the actual decompression of the video.
In my limited tests on low powered hardware the updated heuristic plays at a higher bitrates and the resulting video image is clearer. The dropped frame rate is higher and the CPU utilization is "pegged" -- but for the most part the problems are not so bad as to cause audio drop outs.
The attached .ZIP file contains both the updated source code for "SmoothStreaming.XAP" as well as a compiled copy.