This WSJ video about the new GPS enabled New York City taxis includes a discussion of paying with credit cards or debit cards rather than cash. There are also some brief screen shots of the passenger interface. As with all electronic payment schemes, generational differences in payment preferences come into play: the older couple featured notes that "We'll pay the taxi with cash only because we always have."
Watch for yourself (the payment discussion starts at min 2:06)
Or view on the WSJ website (if your RSS reader does not support video).