Quick Tap is enabled at 50,000 stores in the UK and for purchases under £15. Here's the official press release and their overview page. The introductory video is below.
The Register gives the service a hammering (El Reg pays by phone – mmmm, free cookies! - a strange headline, but it appears that although the Register's journalist munched the cookies, there was no sign of the transaction in Barclaycards's transaction log!).
The poor reviews doesn't fault the payment process (which appears to be seamless /magical), but the initial setup and configuration of the payment mechanism on the phone and then the ongoing account management.
In conclusion, El Reg reports:
It will be a few months before anyone else commits to using the system, and we're not convinced the infrastructure is quite ready yet despite the point-of-sale process working so well. Proximity payments from phones will happen, and Quick Tap is the first in the UK, but like most first movers it's more than a little rough around the edges.