If you're new to the platform, the best thing you can do is go to WWDC this year. Yes, it's expensive, especially if, like me, you no longer live in the Bay Area (or perhaps, never did). But WWDC is an unparalleled chance to learn about the iPhone. There will be a huge number of sessions and hands-on labs, and it's a great opportunity to meet other programmers. The labs are an unparalleled opportunity to have your code looked at by Apple engineer.
If you are a company looking to build iPhone apps or port your existing apps to the iPhone, you really, really, really, really (and really) should send your iPhone programmers to WWDC. The return on your investment will be astounding. Don't bother sending project managers or non-technical folk - this isn't a marketing, lovey-dovey kind of convention. This is a hardcore technical crowd, but there's an awful lot of smart people there and a lot of good information to be gotten.