In a few days, The Apple App Store will hit 25,000,000,000 downloads. They're making a grand promotion out of it, even giving the "winner" a $10,000 App Store gift card. If you check out the Wikipedia article on The App Store, you'll see that it was initially opened July 10, 2008. Within 3 years, the 10,000,000,000th app had been downloaded. Lets put some of these numbers in to perspective.
If we converted downloads to seconds, 10,000,000,000 seconds ago, it was 1695. The Bank of Scotland was founded that year. 25,000,000,000 seconds ago? 1219. That's almost 800 years ago.
Converted to grains of rice, 10,000,000,000 grains has a mass of 1.4 x 106 pounds. 25,000,000,000 grains? 3.6 x 106 pounds. That's enough to feed 15 million people a days serving of rice.
The App Store hit 10,000,000,000 downloads in only 926 days; that's almost 11 million downloads per day or 125 per second. Based on those numbers, it shouldn't hit 25,000,000,000 until November, 2014. As of 1pm EST on February 24, 2012, they had 24,638,985,412. That's 18.6 million downloads per day or 215 per second. That's an increase (overall) of 172%. By that growth rate, 50,000,000,000 should be right around the corner!