If I started a site to sell redeemable Mt. Gox codes printed on a physical card and mailed it with Signature Confirmation, would that eliminate the possibility of chargebacks?
if you were shipping barbie dolls or other physical goods and were following the terms in paypal's seller protection list, then the recipient's claim of "item not received" could be challenged by you. bitcoin whether printed on a physical card or sent electronically is still a digital good, and as such that releases paypal from honoring this seller protection guarantee.
you can try it, though dealing with paypal has only ended in tears for any sellers with any volume to speak of.