This vending machine is actually a proof of concept system for wireless paying. To buy a gumball you send a payment to a website that returns a QR code. You scan the code and then the machine Tweets your purchase and spits out your gumball.
Ray Tanaka and his crew at PayPal Labs hacked together the multi-part system using a mechanical candy dispenser, a couple of Arduino Duemilanove, a WiShield, relay, proximity sensor, and LED display. The end result allows you to scan a QR code, make a payment, and acquire munchies using a smartphone. As you make your payment, the machine will tweet your purchase and notify a confirmation display.