Via oreillyradar:

NFC by itself won’t be big, but NFC combined with smartphones and awesome software could be huge. Here’s an example:

Because many of these systems are new, there is often a limited number of places to buy a card and/or add value, especially outside the city center. This presents a great opportunity for NFC-equipped smart phones which, in addition to being able to read cards, also have the capability to emulate a card. No matter how far to the edge of an agency’s service area you are, it should be possible to download the ORCA or Clipper app and hop the next bus, streetcar, train, or boat. Apps could link with existing payment infrastructure such as Google Checkout for quick payments without additional setup, and for international travelers looking to get around, apps could support multiple languages and automatic currency conversion.

Related question: Will you use mobile payment?