The latest milestone for the App Store was released by Apple on January 5th, surely not timed to interfere with any Google Phone (or HTC Nexus One) announcements. In the press release by Apple, the company noted that the App Store has now passed 3 billion (with a b) downloads.
The App Store was launched with iPhone OS 2.0, approximately 18 months ago. Since then, it has surpassed 100,000 applications, and reached the 1 billion download mark in April and the 2 billion mark in November.
Based on those numbers, there's an obvious trend of increasing speed at which these milestones are being met. Apple CEO Steve Jobs said:
“Three billion applications downloaded in less than 18 months—this is like nothing we’ve ever seen before. The revolutionary App Store offers iPhone and iPod touch users an experience unlike anything else available on other mobile devices, and we see no signs of the competition catching up anytime soon.”
Others have tried to emulate the App Store (e.g., Android, BlackBerry, Nokia, Palm), but none have close to its success yet. It would be interesting to know how many apps for jailbroken iPhones have been downloaded, as many users, though still a minority, have jailbroken their iPhones in frustration over Apple's App Store policies.