Should UPS worry about Amazon's Drones?

(7/29/2015) I think worrying Amazon's Drone flyers will replace UPS in the US exaggerates its potential impact. How many houses will be able to be delivered by Amazon Drone fryers? How heavy could a flyer carry? What's the dimension it can carry without worrying balancing issues? How geographic density can Amazon build operating offices to handle drones?
      UPS drivers delivery and pick up packages in Milk Runs, which mean UPS can drop off can pick up maybe 100 times along all its way for an 8-10 hour shift. Can Amazon Drone do that? Or it always needs to return back to the center to do the 2nd, then back again for the 3rd delivery? All drones' back flights are empty loads. How many trips can Amazon fly in one battery charge? City might be good for Amazon? But the air space in the city is congested and difficult to navigate and the rent and facility cost will be expensive. After thinking of these issues, I think UPS has not much to worry about YET.