There are 125 NFC transactions in the UK every minute

"Visa has announced that contactless payments have reached “tipping point”, with 1.5 million contactless bus fare payments made in London since December. One in four of the 26.9 million UK Visa cards now uses contactless technology and use grows by 22 per cent every quarter.
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“We have seen cases of mischarging in just a dozen instances,” explains The UK Cards Association’s head of policy, Richard Koch. “There are 125 NFC transactions every minute, or about 70 million a year, meaning these cases are really few and far between.”
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Some of the problem is lack of consumer awareness. Although contactless payments are on the rise, ePayments software company Compass Plus says its surveys show 40 per cent of British consumers still have no idea about the technology.
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Cash payments are being displaced. The UK Cards Association says the average debit card transaction is £40, while on a contactless card it is £5.50, with many payments of much lower amounts."

Source:  Evening Standard, 3rd June 2013

Note - this article is all about card payments (& potential errors in charging), not mobile payments