It would be nice to be able to convert the State and Country sub-fields to dropdowns, with the option to encode the values (e.g. Texas as "TX", United States of America as "US"), as well as the ability to pick a default. Obviously these things can be done with JavaScript (which is what we have been doing) but they seem so basic that I feel they should be part of the field options.
If you want to go the extra mile, add a way to integrate with Google Maps or similar address auto-complete service.