CPM is just to easy for advertisers to inflate CPM numbers without any promise of quality ... The combination of CPC and Placement reports and advertisers have the tools to help balance out the equation.
This sentiment is echoed by the community. CPC is the way to go:
CPM is an uncontrollable nightmare; and text ads rule. The other stuff (radio, print, etc.) is nice to have in the arsenal, but only as add-ons. I think CPC will continue to be the heavy hitter for a while.
Essentially, CPM doesn't seem to fare well for anyone. CPC is more work but it pays off.
This should play out pretty well over time.
Forum discussion continues at Search Engine Watch Forums.