1. For the counties that don't require a state/region we will disable the required field validator.
2. The cart doesnt send an api call to the usps web service until you click calculate shipping button so there is no way to eliminate the shipping methods prior to the user clicking calculate shipping. To eliminate shipping methods when a country is selected we would have to program the selected index change event of the country drop down to call the usps web service causing a post back on the page and delay to the user. Since the user gets the correct ship methods returned when they click calculate shipping not sure it would be a good idea from a user experience/performance perspective to call the usps web service twice within such a short time span but we will evaluate it.
3. If a customer selects a shipping method and clicks calculate shipping and shipping method they selected is not available for their destination address the cart simply returns the ship methods available. I think its fairly intuitive to a user that the ship methods returned are the ones available but I can see your point that it would be helpful to display a message we will look into it.
4. USPS made an unannounced change to their international rate service and added a registered trademark symbol after all of their international rate names for some reason. This caused the SC rate calculator not to display the international usps rates. We have a hotfix ready if you send an email to support@smith-consulting.com we will email you the fix.
Thanks for all your great feedback!
Dave