I remember when the Ad Program first started, the CPM was as high as $11. Now it averages around $4-$5. It sometimes jumps to as high as $7, but not much higher. I didn't realize HP could control the CPM. I just figured it was "market forces" determining it. But if it was as high as $11 when the program first started, that gives the impression that there was some manipulation going on to make it appear the program was more profitable than it actually is.
I don't hang out at the forums much but if you post there, I'll check it out. I'd like to see what other folk are saying since HP tends to lack transparency in these matters.