From what I know there is no currencies in the world with any "backing".  All are fiat currencies, not much different from Bitcoin.  At least bitcoin has the backing of "electricity and CPU cycles".  The rest of the currencies are just pieces of papers which depend on the confidence of the investors in them.

I would humbly disagree with you here. The public key is made available to the world so amazon cannot deny that the key is is wrong since they will put it in global circulation. The maths and technicalities are complicated, granted, but thats why its equivilant is forensics. But true, anonymity cannot be guaranteed with Bitcoin, especially when you buy stuff in the real world, its just very difficut, not impossible. You can go through the delivery company check their records to see if it had been delivered.

'in this hypothetical situation when you buy a book of Amazon, Amazon can provide you a receipt with unique bitcoin address and delivery address, signed by its private key. then you will be able to prove that the payment has been sent to that address, but the book has not been delivered (and it doesn't matter who ordered the book, paid for it or was going to receive it)'

Very technically clever but instantly the entire system then fails to be 'anonymous' if Amazon refuse to accept the key is correct. Also just to further bring you into reality - you would have to provide an address for them to send the book to.

You guys are living in an entirely theoretical world. Wake up.

I ruin about 1 in 10 of the stickers, so they may have gone to nobody.  I asked for the strongest adhesive and the most tamper proof hologram and that's exactly what I got.  At least 1 in 10 times, I ruin the sticker just peeling it off the original backing, exposing the "honeycomb" tamper-evident grid, as the tamper evident pattern is literally hair-trigger sensitive.  There is absolutely NO FREAKING WAY anyone is going to get those stickers off without making the honeycombs visible, and if I have to throw away a sticker, the address is thrown away too.  So, at least 1 in 10 chance you may have sent 0.001 BTC to the bees.

Isn't this just a resource which assists counterfeiters?
Without this list - counterfeiters would need to re-use addresses from a small pool in order for their coins to pass the basic 'public-address shows value in blockchain' test.

What is the motivation for publicly releasing this list?   Are you likely to do this in future?  (I'm hoping not)

Even if you have no intention of maintaining any sort of dupe-public-key tracking/reporting app - someone else might want to, and having a list of *all* released coins might reduce the usefulness of that.  Being able to verify a key by search once you know it is fine - but I don't think they should be listable.

1 - I chose a hologram with the name Casascius on it, because that would be prohibitively expensive ($thousands) for someone else to duplicate.  And if they're going to go to the effort, they may as well make their own legitimate coins (clearly there's a demand) rather than perpetrating a fraud that would get quickly found out.

2 - Each coin has the first 8 characters of the bitcoin address on it, which is enough for Block Explorer to find it.  When I load bitcoins on coins, the transactions are fairly distinct - lots of outputs of 1 BTC to lots of addresses wrapped into a single transaction.  So if someone were to vanitygen one (the odds of it happening purely at random are 2.2 trillion to 1) you could find the right transaction.

3 - it becomes a piece of metal, not quite as desirable, but still cool nonetheless.

4 - I could probably put together QR codes, but I favor readable codes for several good reasons, the most significant being that most people don't know how to scan them into a program without retyping them anyway (typical joe will scan with his iphone and type into his computer what he sees on the screen, defeating the purpose).  And second, if the code gets torn or damaged, your eyeball will do a much better job of piecing it back together than a phone that will just say it can't read the code.

5 - Probably no smaller amounts.  Maybe bigger amounts (such as 10 or 50 BTC in larger, more ornate coins).  This is fairly time consuming for me as it is, and I fear that demand could outstrip my ability to supply them.  It's hard to want to delegate it, as I can make sure that all of the codes are legible and correct and match the address on the outside, but somebody else might not take that so seriously.

6 - Others have asked about durability.  I don't know yet - haven't had them that long.  The adhesive is quite strong and they will probably resist water just fine, but what would really ruin them is if they sat in your pocket and got jingled around with your keys.  I would treat them as delicate until proven otherwise.  I am experimenting with spraying on a layer of polyacrylate which adds significant protection to the hologram, particularly at the edges, but it will take me several days to really know for sure how that will end up.  Seriously though, I hope somebody copies my idea and does a better job and makes a wash-proof key-proof bullet-proof coin for less

Chance alone is very unlikely, but I'm willing to pgp sign a list of all the Bitcoin addresses used in this project.