I think the google checkout announcement has some interesting implications for AdSense. What keeps google execs up at night? Click fraud. Google has to refund for bad clicks, they're getting sued over fraudulent clicks, and stories of fraudulent clicks drive away advertisers. Its a big risk for them. What is the best way to please advertisers and discount fraudulent clicks? Their solution is ROI tracking and its companion, smart pricing. Google wants to charge less and pay out less for fraudulent or low quality clicks so that advertisers will spend more on adwords. I think the primary goal of checkout is ROI tracking. According to the New York Times, google will be losing money on the transaction fees for google checkout. Not only that, but there is a rebate on transaction fees for AdWords users, losing more money, but promoting the use of both services together. Why would they set it up this way except for tracking ROI? More and better ROI tracking means more and possibly better smart pricing. Have you ever wondered why smart pricing is tracked on a per account basis. Perhaps it is because they want to track click fraud on an account basis? Or perhaps they cannot collect enough ROI data to do it on a per site basis? Can google checkout change that? What impact to you think Google checkout will have on AdSense?
Google checkout accepts all major credit cards - visa, mastercard, discover and amex. The Citi thing is just some kind of special promotion.