I'm running the hg tip release and the Google Checkout payment module never emits an order_success signal. This has resulted in gift certificates not getting generated and having to listen for an satchmo_order_status_changed signal instead of an order_success signal.
The trigger for an order_success should be when Google returns a charge-amount-notification where the total-charge-amount is greater than the order total cost. I tested this fix with equal to and it doesn't trigger an order_success. This may have to do with Decimal accuracy?
I've attached a diff to handle this case and call order_success().