Currently, I have Winamp 5 streaming my favorite MP3 music on my comp, while I am typing this. AVG anti-virus ia also running in the background.
So at the moment I'm doing at least 4 things at once: surfing the internet, listening to streaming MP3 music, downloading a software update for Windows XP, and running an anti-virus program.
For monitoring, I 'm running Dr. Speed, a Win XP program that came with my MB. This monitoring program informs me of my core and system temps in realtime. With CPUIdle running in C2 mode, my core temp is showing between 28 C and 32 C, with all those programs running at once.
Now when I unload CPUIdle, in less than a minute my core temp shoots back up to 36 C - 38 C. When I reload CPUIdle, it quickly goes back down to the sub 30 C temp range. So I know without a doubt that my computer would be running significantly hotter WITHOUT the CPUIdle software.
To me, that is proof positive that this program does exactly what it is designed to do. And it works while the CPU is under load, not only when it is idle. Keep in mind that I also utilize hardware cooling methods (ie: several case fans running, using rounded IDE cables, etc.) in addition to the software method to keep my CPU cool, so your results may not turn out as good as mine...
The Linux OS has utilized this kind of software cooling method for years, as a built-in function, so its not like its anything new or groundbreaking.
ANY OS or software program can take advantage of the modern processor's ability to accept what's known as HLT commands, to keep the processor running cooler, if said OS chooses to!