We are selling a digital good that requires an optional physical shipping address to be captured. But the checkout page still should not ask for a shipping method, such as FedEx UPS. The only steps should be billing address, optional shipping address, and credit card and order review. Billing address should be asked first, with the option to branch into asking for a shipping address. If billing and shipping address is the same, give the user the option to skip that. Also these addresses should be saved in the My Account under their address book.
This is all very similar to the standard Magento checkout, but the trick is to make a digital good ask for a shipping address, but not a method.
We are using a one page checkout page, and we are open to solutions on how to accomplish our goal. We are looking to get this finished quickly, and I will be highly available though chat and Skype for discussion.