>
> This happened to one of the merchants at the Bitcoin 2013 conference in
> San Jose. They sold some T-shirts and accepted zero-confirmation
> transactions. The transactions depended on other unconfirmed transactions,
> which never confirmed, so this merchant never got their money.
>

Beyond the fact that this risk can be priced in when enough data is
available, I'd be interested to talk to this merchant and dig into what
happened a bit.

For example:

   1. Was the dependent tx non-standard?
   2. Was it double spent?
   3. Could a wallet have co-operated with the P2P network to detect and
   flag whatever the issue was?

My own experience has been that when this happens, it's usually not the
result of outright maliciousness (especially not at a Bitcoin t-shirt
seller at a Bitcoin conference!) but rather something messed up somewhere
and the software in use just didn't detect it well enough.