As a developer, i would say iAd is a very good incentive given by Apple to its developers. I have been using both admob(google) and iAd in my iPhone Applications, and i have seen iAd pays me 10 times or even more sometimes than Admob pays me, the eCPM for Admob is 0.25 to 0.30$ but for iAD its 5$ to 10$ , you do the math.