Apple emails about a new release of the iPhone SDK:
Log in to the iPhone Dev Center and download the third beta version of the iPhone SDK.
Make sure to take advantage of all the development resources available to you in the iPhone Dev Center, including updated documentation such as the iPhone OS Programming Guide, a new tutorial for creating iPhone applications using Interface Builder, and the latest release notes.
So I don't always agree with the way Apple does things, but I'm heartened to see them revving the iPhone SDK so quickly during the beta. They also really seem to be doing a great job of documenting things.