Google software engineers Jesse Alpert and Nissan Hajaj:
Even after removing... exact duplicates, we saw a trillion unique URLs, and the number of individual web pages out there is growing by several billion pages per day.
...This graph of one trillion URLs is similar to a map made up of one trillion intersections. So multiple times every day, we do the computational equivalent of fully exploring every intersection of every road in the United States. Except it'd be a map about 50,000 times as big as the U.S., with 50,000 times as many roads and intersections...
Whoa. One trillion? To give that number a little perspective, one trillion dollars is more than The Anchoress makes off of her blog ads in a month!