Gregory Lyons, a senior analyst at iCrossing has pointed out that the growth in the US and UK have reduced but popularity in countries like India and Brazil continue to expand at an amazing rate.
With only 3% of India’s population on Facebook and 16% of Brazil’s (compared to 49% of America’s population or 47% of the UK’s population) countries such as these will clearly contribute heavily to Facebook’s continued growth.
As Facebook continues it's growth towards becoming the world's phone-book. The 1 billion users is definitely a milestone in the right direction.