Receipt has got a flaw. As a merchant I won't be sending receipts of funds without any confirmations. FYI ![Wink](https://bitcointalk.org/Smileys/default/wink.gif)
![Wink](https://bitcointalk.org/Smileys/default/wink.gif)
I would urge you to return a receipt with a memo that says:
"your order will be shipped as soon as your payment has three confirmations."
Explicitly telling your customers what they can expect to happen next is a great feature of the proposal, I think.