While growth in the United States has slowed tremendously for Facebook (flat to slightly down in the last quarter through end of March 2012), a three-year trend is instructive. During the time from April 1st 2009 to April 1st 2012, Facebook added over 96 million users in the United States (+161%). The optimal growth rate of course is for Brazil with 10879% growth from only 402k to over 43.7 million! Here’s the overall figures for your reading pleasure.