A couple of weeks ago it was brought to my attention that Google had recently added a filter to the OneBox that sometimes appears on their SERPs when you search for products.  The filter lets users view only the results for their product search that come from merchants who accept Google Checkout.  Some cried foul.  And until now, there hadn't been an official mention from Google.

The Google Checkout blog has written a post explaining two "experiments" the company is running in regard to Google Checkout:

• The first experiment involves adding buttons to AdWords ads from merchants using Checkout.  In the past, Google had identified these merchants with a small, blue Checkout icon.  That icon has been replaced with a button.
• The second "experiment" involves the search filter mentioned above.  Google says it got a lot of positive feedback about a similar filter that was added to Froogle a few months back.  In response to that feedback, the search company has expanded the filter to traditional search results.

For starters, I notice that Google explicitly refers to the AdWords buttons as experiments:  "The experimental badge we're testing."  However, the description of the search filter lacks the use of the word "experimental" so I'm guessing this change is less of a trial and more of a permanent addition.

Whatever the status of this change, one thing is certain:  if you sell online, it might be a good idea to start accepting Google Checkout.  This is quite obviously Google's motivation.