Mike, would you consider having a buy back guarantee for the face value of any casascius coin as long as the hologram is intact and genuine?
Formally? I'm willing to formally guarantee that I have appropriately handled and destroyed all copies of the private keys because I can easily control that. And that if you bought one from me, that I have sold you an honest coin.
Regarding the physical coins themselves? I'd say informally at best, only to stay reasonable, since nothing is 100% unbreakable. The coins are made with a reasonable standard of care for a 1-guy hobby project given the budget I put into it. That said, if you've got one, I'll probably buy it from you.
Beyond that, I don't have the means or the practical ability to test the physical coins with every kind of ray or chemical or imaging technology out there, so if someone were to find an exploit that allowed the private key to be read on my coins without ruining the hologram, I would be more likely to make a posting or a statement that such had occurred, so everyone would know that they need to protect themselves from it, rather than buy back all the coins. Of course, any announcement like that would be unfortunate - but given that the coins are collected far more than they are circulated, that would be only a letdown, rather than a major vector for transactional fraud. I assume people would keep their coins like they probably already do, and would have nothing to worry about with respect to their own coins.
If I were to formally guarantee the physical coins, then at any point an exploit were found, that guarantee would amount to an invitation for people to exploit the BTC off and then redeem the guarantee sell them back to me, and that's inconsistent with my goals for the project. I believe the coins are reasonably secure, but I expect that as Bitcoin becomes more prominent, that there will be advances in the security of physical bitcoins produced both by me and by others, as well as the attacks made against them, and the first iteration of the physical bitcoin definitely won't be the last.
If coin material (such as unused holograms or unfunded coins) were to be lost or stolen, I would probably make a judgment call. For a small amount, I would probably offer to redeem them for face value. For a large amount, I would probably announce that the material had been stolen, provide any information that identifies the stolen material, and then probably use a new design that is clearly distinguishable. Keep in mind, the project is to promote Bitcoin, promote a proof of concept, and provide a neat-looking example of a good honest coin... but not to insure against things I couldn't possibly reasonably control. Fortunately, to my knowledge, there have been no occurrences of this kind to report, and to the best of my knowledge, all coins in the wild are either legitimate and funded, or (at worst) are waiting to be funded when enough time has elapsed to ensure they've cleared customs of their buyer.
