I have google checkout and paypal express checkout working on 1.3.7. I had a customer use the google checkout. It worked fine then. Here are the problems I see with Google Checkout though:

1) I offer insurance as optional. I have created a table and flat rate but the customer will not understand that the table rate is with insurance. Basically, the customer is not seeing the optional order additions.

2) Only 1 shipping option allowed... 1st Class (or priority or express), .... while Priority and Express are unavailable. The customer doesn't really know which shipping they are getting either. I have tried to create shipping files based on the tables.php but get a message
Warning: reset(): Passed variable is not an array or object in /home/xxxxx/public_html/admin/modules.php on line 279

Warning: Variable passed to each() is not an array or object in /home/xxxxx/public_html/admin/modules.php on line 280

I guess it wouldn't work even if I was able to install them?

I guess for now I can put some text on top of the button trying to explain the table vs. flat rate.... don't know how well this will work.

3) I am going to pull my hair out if one of my international customers pays with my US 1st class mail rate.... the Google Checkout module should have the option of allowing for a payment zone like paypal express checkout does.

I think Google Checkout should come back to the cart and finish the order, thus allowing the proper shipping and order additions to be included, if not this then it should allow more shipping options with descriptions.

I can send my \includes\templates\my_template\templates\ files to a zen cart support person if they would like to post them.