Hmm... I guess I was too slow:
"PAYMENT TIMED OUT! We didn't receive a payment from you. Try again."
I copied the generated BTC address, but forgot the amount by the time Bitcoin launched, so sent you 1.11 (eleven is my favorite number) bitcoins.
Now I didn't get whatever it was I paid for.
Definitely cool, but also definitely clunky. Where this needs to go, in my humble opinion:
1. MyBitcoin should get rid of the CAPTCHA for most users (do the Google thing, and only show the CAPTCHA if it detects potential abuse) (oh, you didn't know Google search does that? Yup, they do, if you do enough weird-looking searches quickly enough you'll get a CAPTCHA...)
2. Bitcoin needs a 'refundtransaction' feature, to get rid of the scary "Do not ever reuse a temporary payment address or your Bitcoins may get lost" warning. Sending to an old address should just do an immediate refund.
3. I want to be able to put the payment address into MyBitcoin and see the status of my payment.
4. Gotta get rid of the "memorize the amount and then copy and paste to Bitcoin" (need a bitcoin-payment-request MIME type, in my humble opinion).
5. Gotta improve Bitcoin startup speed; at the very least, make the UI come up quickly while it re-verifies the block chain (I think that's what it is doing...).