It just struck me that another very good use of this service (and perhaps a reason for orders being cancelled by Amazon when it doesn't work) is for people trying to drain money from stolen credit cards or hacked Amazon accounts.
Normally the problem with buying online with a stolen card is that you have to actually receive the goods, which means being tied to an address. Here you can send the goods to someone else's address, and get (reasonably) untraceable bitcoin in return.
Purse risk becoming (not necessarily through any fault of their own) a high tech online fence. And Amazon may get fed up of being drawn in to that.
Hadn't thought of that, but that's a fair point. I'll bring it up with Purse to see if there is a way to safeguard against that, perhaps by enabling Amazon to interact with the escrow process or something.