Now Google tests something that will definitely attract your attention, in case you were not aware of this Checkout thing: replacing the small icons with big buttons under the Google ads.
Here's an incomplete evolution of the way Google promotes Checkout in the AdWords section:
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{ Thank you, Ted P. }
Update (February 13): Google announces that the big badges are here to stay. "We expect the new image to help shoppers more easily identify Google Checkout merchants. We're also putting the shopping cart badge on ads in the Google advertising network."