The rules for flying radio controlled aircraft are under tremendous debate and change, mainly because of two new technologies that have together created a new business. The technologies are tiny flight management systems costing about $100, and excellent lightweight cameras like the GoPro (invented by a UCSD grad). The new business is using drones for low-altitude photography (and eventually for other applications, although IMO not for package delivery).
Congress put the Federal Aviation Administration in charge of figuring out what rule changes are needed. So far it has done a slow and weak job. (One result is that the U.S. has lost leadership of the industry, and may even become a backwater. That is a topic for another day.)
Pilots are instinctively concerned about risks to manned aircraft, from unmanned aircraft. Much argument back and forth has ensued, but there is little or no modeling or investigation. (What happens when a 2 pound quadcopter collides with small plane at 140 knots? Apparently there have been zero experiments on the issue.) Here is an interesting blog post on this issue.
My take on this issue is that the likelihood of serious air-to-air collisions is tiny. Far fewer than bird strikes, for example. A much bigger sour of injuries will be untrained idiots flying drones over crowds of people.