Apple has revealed that by 200,000 iPhone developers have downloaded Software Development Kit (SDk) so far. Apple plus announced that in mid-March, the iPhone SDK had been downloaded 100,000 times. According to Apple CFO Oppenheimer Apple is signing up more developers each week.

More than 400 higher educations are now creating applications for the iPhone, and more than one-third of Fortune 500 companies are actively creating software for the iPhone as well.



References:
http://www.macworld.com/article/133146/2008/04/iphonedevs.html