As I understand it, BC has 10 second confirmations and you wait for 10 confirmations to be sure it can't be reversed. This is correct? So a payment at a retailer will be confirmed without risk to the retailer in 1min 40 seconds?
Receiver will have to decide how many confirmations he needs before the payment is considered accepted. If you buy a cup of coffee, it is possible you wouldn't require confirmations at all. When buying something more expensive you could require 20 confirmations. Or if the buyer looks like he can run fast, and there is little distance between the register and the street door.
There is no magical number of confirmations after which the risk disappears totally, but it is reduced after each one. At least that's how I've understood it.
EDIT: haha this thread runs so fast that as soon as I've finished writing my reply there are already 5 answers.