Here's a idea for an easy revenue stream for Google: replace the "I'm feeling lucky" button with a "Search Amazon.com" button. When a user clicks that button, it takes them to the Amazon search results page. Extrapolating from what my site earns me in Associates fees each quarter, Google would stand to make several hundred thousand dollars a quarter without devoting any people or energy into extra development. Since the button would have such prominent and permanent placement on the site in comparison to the Amazon links on kottke.org, the amount would probably be much higher, maybe a million a month or so.
Of course, what's more likely is that Google will create something akin to Amazon Light at shop.google.com or something, putting Amazon's database into Google's user experience. Google would probably be just as clever as Amazon in offering shoppers useful ways to browse merchandise...and they wouldn't have to deal with the order fulfillment or any of the other stuff. They'd just have to sit back and collect the Associates fees.