Yea well, I've been in that adCenter program for over a year, and I keep going back and testing it from time to time, and it doesn't do squat. The ads just aren't there. I am hoping once the Microhoo merger completes (some time late this year) and the Yahoo advertisers are there it will improve, but as of right now, I've given them tens of thousands of impressions and not earned a penny.
They do have some ad formatting and targeting options I really like, and if the advertisers *do* ever show up, Google will have sit up and pay attention.
But not yet.