Apparently 14 pence from every £1 (100 pence) paid in fares goes on running London's RFID Oystercard system, and this cost helps explain why Transport for London are so keen on seeing people using RFID equipped bank supplied debit and credit cards when paying their fares.
Personally my concerns are that anonymous paper ticketing will eventually be phased out - or made even more expensive, as it already is for some types of ticket.
This is an issue which affects all of London's transports - trains, trams, buses, etc.
Simon
http://www.busandcoach.com/newspage.aspx?id=6138&categoryid=0 http://www.busandcoach.com/newspage.aspx?id=6138&categoryid=0

Assembly concerns on cash card ticketing

The London Assembly says that Transport for London must guarantee that its plans to introduce contactless ticketing with credit or debit cards will not disadvantage people who choose to stick with the existing Oyster smartcard. The Assembly?s transport committee also questions the robustness of TfL?s business case for the introduction of contactless ticketing, concluding it is unconvinced the scheme will deliver the financial savings TfL claims.

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Caroline Pidgeon, the transport committee?s chairwoman, says: ?It?s only right that Transport for London is looking to new technologies to enhance its ticketing offer, but many passengers are sceptical about using bank cards as tickets, and others simply won?t be able to.

?If contactless payment is to prove successful we would expect to see a far more detailed and compelling case for its introduction. Most importantly, we want guarantees that all passengers will continue to have access to the cheapest fares no matter what type of ticket they use.?