Wait, what problem is this supposed to solve? You don't have the "fast transaction problem" when ordering things online.
Yup, payments show up instantly and are probably good for most cases. No need to wait for confirmation. But how in the world can I buy a 2000 BTC car without waiting an hour! 
That's not the point. Online, you'll have plenty of confirmations long before the product gets into the UPS truck. (If you're selling digital products like e-books, then you have to wait for a confirmation or take your chances.) For transactions conducted in person, the seller simply needs to be reasonably sure that you didn't attempt a double spend attack - which itself requires careful timing and some luck along with >50% of the network. And in any case, if you tried it on the car dealer, they could just call the cops. After all, they know who you are anyway.
