For merchants using Google Checkout, it's time to look around for an alternative, as Google has announced it is discontinuing its payment system to focus on Google Wallet. It seems that the existing APIs won't be continued, and there is no direct replacement. Effectively, Google is stepping away from payment for physical items.
Six months seems rather short notice for such a major change, but we guess this is the danger of relying on a company like Google with its fingers in lots of pies. They can decide to refocus at the drop of a hat, and a service you rely on is suddenly history.
More information:
https://support.google.com/checkout/sell/answer/3080449