Here's a good summary of the SDK presentation:
http://www.engadget.com/2008/03/06/live-from-apples-iphone-press-conference/
SDK beta out today and iTunes App Store opens in June along with firmware 2.0. Rumor is that a 3G iPhone may surface at this time as well.
Jobs stated that 71% of web mobile traffic is via iPhone, but I didn't get a source.
Should be fun stuff in a few months.
Best,
Kurt