Feb 19, 2016 was the deadline for existing drone owners in the US to register their drones. According to Motherboard (http://motherboard.vice.com/read/what-happens-if-you-dont-register-your-...), "Registration is mandatory for all pilots owning drones weighing more than half a pound, and costs $5. It also involves adding your name, address and contact information to a government database, which will soon be publicly searchable by an FAA-assigned registration number via the agency's website."
Not everyone agreed with the registration.
"The rules, introduced by the Federal Aviation Administration in December, have been harshly criticized by hobbyists, who see them as a disproportionate crackdown on a technology whose dangers have been routinely exaggerated....the Academy of Model Aeronautics, a hobbyist organization for RC aircraft, advised its 185,000 members in the US to hold off registering."
What about all those who didn't register?
"The FAA's rules say that pilots failing to register could face up to $277,500 in civil and criminal fines and/or as many as three years in prison."
In reality: probably nothing will happen, but that's just conjecture.
The FAA is getting hit left and right with lawsuits over the registration. From the number of registrants reported, (around 342,000), it looks like we're not even close to the 1 million estimate. If you haven't registered, you're in good company.