Just to put it all in one place:
Today's FAA news release announcing Interim Final Rule (IFR) :
https://www.faa.gov/news/press_relea...m?newsId=19856
About half way down, there's a hyperlink to the registration website (which goes live on 21 December) :
http://www.faa.gov/uas/registration/
One link there is a FAQ. The third link, "Registration and Marking Requirements for Small Unmanned Aircraft Interim Final Rule," is a link to the actual FAA document that establishes the policy that is the subject of the news release. It also discusses, in great detail, all the comments received as well as generally the FAA's reason for accepting or rejecting them.