Product Search is also a great vehicle for Google Checkout, the payment service that still needs a lot of promotion. As you can see from the screenshot below, there's so much Google Checkout in Froogle, that you start wondering if the entire service is an ad.
Google Checkout also has special offers (savings, free shipping, frequent flyer miles) for consumers, in addition to more than a year of free processing for merchants.
Google indexes all the reviews from Google Checkout users and adds them to Product Search (e.g.: reviews for SnowandWater.com).
As the stores who use Google Checkout gain more and more visibility in search results and ads, Google hopes to pressure the rest of the merchants to accept Checkout. Users are trained to look after the Checkout badge because they'll buy things faster and more conveniently.
Even if Google appears to lose money in Checkout, the future could bring a bigger spending in AdWords and happier / more loyal users. To achieve this, Google added a link to an unpopular service to the homepage and cluttered search results and Product Search with Google Checkout badges.
Google's fast and frugal checkout makes Google more powerful because you trust it with information about your credit cards and the things you buy and because you finally allow Google to finish the process of obtaining search results with a genuine confirmation: an acquisition.