Kiva Systems already makes a warehouse robot. I didn't know if Amazon used them or not, so I did some quick Googling and it turns out Amazon bought the company! http://dealbook.nytimes.com/2012/03/19/amazon-com-buys-kiva-...
other research groups (e.g. http://rpg.ifi.uzh.ch/) are working on bringing this technology out of the motion capture system by mounting cameras on the drones and use image processing algorithms to estimate the drones trajectory.