How Much Information? 2003 is a new version of How Much Information? 2000. They both try to estimate how much information was produced and in what form (from magnetic media to film.) These reports are thorough and fascinating.
Some of their key findings:
Print, film, magnetic, and optical storage media produced about 5 exabytes of new information in 2002. Ninety-two percent of the new information was stored on magnetic media, mostly in hard disks.
…
new information stored on paper, film, magnetic and optical media has about doubled in the last three years.
…
Information flows through electronic channels — telephone, radio, TV, and the Internet — contained almost 18 exabytes of new information in 2002, three and a half times more than is recorded in storage media. Ninety eight percent of this total is the information sent and received in telephone calls – including both voice and data on both fixed lines and wireless. (Executive Summary)
Update, July 2006: The earlier 2000 study has an effective series of charts and graphics illustrating the explosion of information on their Charts page.
This one is originally from the Economist Magazine, October, 2000.