Interesting question, isn't it?
I personally downloaded over 1,000 apps in 2 years of playing with my iPhone. Most of them were eventually deleted, but I kept track of the numbers on my computer.
I recently received a link to a great presentation reviewing the latest statistics and trends in the mobile applications world: iOS AppStore, Android Market, BlackBerry AppWorld and more.
It has a lot of known trends and numbers, but also a bunch of interesting figures about apps and mobile users:
Head over to SlideShare and look for the following link for a lot more.