I have a site with a few hundred pages covering a wide variety of topics. The best topics have lots of traffic, high CTR, and high CPM... other topics have low traffic, and still others have lots of traffic but low CTR and low CPM.
For the high traffic/low CTR/low CPM topics, I'm thinking of switching to the Yahoo adsense competitor once they move out of beta and I see some reviews that it works relatively well. I'm thinking that the poor performing topics on my site might be keeping down other topics because of smartpricing. So even if the pages that I switch to yahoo make less money than before, in the eyes of google, my account will seem to be performing better and I may get better ads via smartpricing.