From Apple's site, here are the new SDK features and improvements.

In App Purchase

Allow users to purchase content or services from your application using the Store Kit framework. This new framework handles the financial aspects of the transaction, processes payment with the iTunes Store, and provides your application with information about the purchase.

Apple has seeded iPhone 2.2 Firmware Beta 2 and has enabled google maps street view.  Also included in this beta is line-in audio accessory support.

Apple is now giving free access to the iPhone Developer Program.  The program is available to accredited, higher education institutions in the U.S. and allows universities an avenue to provide official courses that do not violate Apple's iPhone SDK non-disclosure agreement.   Stanford has announced a new class this fall titled "iPhone Application Programming."  You can safely assume other schools will follow.

Here is the list of API changes to the iPhone SDK from 2.0 to 2.1.  most of it is in the Audio Toolbox, but no iTunes/Library access additions.