The usual amount....
....of ridiculous rheotic and ignorance being spouted here.
NFC technology is totally different from GSM, GPRS, 3G, WiFi etc. Think of it more as your Oyster Card with bells on being embedded into the back of your phone. I know Oyster isn't 100% perfect, but it works nearly all the time for almost everyone - this will be the same, and won't be dependent on your phone being in coverage or even switched on.
It's also likely to be free to use - remember that every retail outlet that you use cash in still has to pay that cash into a bank and is charged accordingly each time it does so. There will be an interchange fee between whichever payment partner you use (e.g. Mastercard, VISA, Amex), but that won't be passed on to the consumer. Nor will you get charged by your network per transaction. You might find that a compatible handset costs more in the first place, but that's it.
Advantages? I'd have thought they were fairly obvious - fewer things to carry (all your credit cards could go onto your phone, no travel card needed), never needing to worry about cash / correct change again....