Wow. When I was back in grade school, the population statistics I remember were that the US population was 250 million, and the world population was 4 billion. Big numbers, and I thought, if I could just get everyone to send me a dollar...
Ah, the dreams of youth.
A quick trip to the population clocks at http://www.census.gov/main/www/popclock.html took me by surprise. The US population has just recently climbed over 300 million and the world population is up to over 6.5 billion. Simply amazing. 20% and 60% growth respectively.
I suppose that it's good to keep track of this stuff, if just for the sake of scale. There really are quite a lot of people out there.