This is an impressive number. Actually, lots of impressive numbers: "It took Apple 74 days to rack up these half billion downloads, and 82 days to get the previous half billion."

The number of downloads is accelerating. Here is the press release from Apple.

Also, note that Apple has sold 17 million iPhones and 13 million iPod touch. That's 30 Million devices that can run apps from the App Store. That's roughly 60 apps per device!