Google Checkout - Ohhh so close to being perfect

I used Google Checkout for the first time today (some awesome deals to be had with $10 off $30 at buy.com) and they did almost everything absolutely right:

• credit card number is one big text box, and it auto formats the number
• phone number is one big text box
  
• CC dates are in two text boxes, as they are printed on the card.
• form is short and simple.

Then I got to the last page of the checkout, and the back button broke. Sigh. It's all the more important because I was not testing the back button, but actually needed to use it.

I was amazed at everything else and I hope other checkout systems learn from Google.