The Zynga Platform will use Facebook Connect to gain initial traction and will continue to use Facebook Credits as the mode of payment.

FORBES: Zynga's Platform for Play Aimed at Reducing Facebook Reliance

For the occasion, most of Barcelona's taxi cabs have been outfitted with terminals that let them accept a "tap" from a phone as a mode of payment.

NPR: Wireless Show Expected To Draw Crowds To Barcelona

With the rapid rise in use of debit and credit card as a preferred mode of payment over cash and check, the number of transactions processed by Visa has grown steadily by 10% in the last couple of years, except 2008 when the economic downturn caused transaction volumes to drop by almost 11%.

FORBES: When Visa Hits $92, Don't Say We Didn't Tell You It Was Going There