So if you are having Magento – Google Checkout timeout issues, 404 issues on your uri callback or just can’t figure out how to configure it in magento try this first
Disable the xml post of shipping methods, I don’t know why magento is sending this information twice but it was stopping my system from working.
edit: /app/code/core/Mage/googlecheckout/Checkout.php and comment out the two sections where it has