Quite a milestone, eh? The U.S. now has a population of 300,000,000 (yes, I was a little late snagging the image below). So October 17, 2006 is the date we'll all mentally bookmark until we hit 400 million.
In case you're curious, the world population at this moment stands at 6,550,987,450. Want to keep an eye out for these figures yourself? Check out these population clocks.