The International Data Corp has released The Diverse and Exploding Digital Universe: An Updated Forecast of Worldwide Information Growth through 2011.
According to the report: "But the number of digital 'atoms' in the digital universe is already bigger than the number of stars in the universe. And, because the digital universe is expanding by a factor of 10 every five years, in 15 years it will surpass Avogadro's number." (Avogadro's number is 602,200,000,000,000,000,000,000.)
Read more about it at "Study: Digital Universe and Its Impact Bigger Than We Thought" and "Web Users Warned about Online Exposure."