There's still a problem to solve though:

who's going to accept payments, process credit cards, verify signatures etc.

Just like there needs to be people who do that at Amazon, Zappos, etc... </sarcasm>

Honestly, a taxi with only a Google maps interface and a credit card swiper would be interesting.

No more tipping!

That is currently the most annoying part of taking a taxi when travelling. Why taxi companies are still using technology from 15 years ago for processing credit cards (assuming they even accept them) is beyond me. If dumping the driver makes it easier for me to swipe, the sooner the better.

How do vending machines work currently? :)