THE RULES HAVE CHANGED.
Part 101 recreational [aka Model] operators, flying sUAS, are no longer required to register most drones under 55 lbs. This is because the FAA is not enforcing recreational sUAS registrations.
The FAA is working on a new rule to reflect this.
Part 107 operators, will continue to need to register their sUAS.
This note: Note: Model aircraft operators that comply with all of these operational requirements during flight do not have to register their UAS with the FAA.
Is on this FAA website page: https://www.faa.gov/uas/getting_started/fly_for_fun/
NB: Probably this question should be deleted, and re-asked, given August 2016 FAA regulation changes, and the outcome of a subsequent court case, and yes, ultimately changes to the FAA regulations as a result of that case.