Thom Robbins, Microsoft Director for Developer Marketing, points out a fantastic hands-on lab focused on helping developers create great experiences for customers running their applications in Windows Vista. Here's how the download page describes the lab:
Microsoft has put together a Hands-on Lab designed to educate developers on known Microsoft Windows Vista application compatibility issues. This process will walk the developer through specifics, focusing on solutions that will enable customers running your application to have a better experience on Microsoft Windows Vista. After completing this lab, the developer should be able to determine if and how the most commonly known application compatibility issues could affect their specific application.
If you're a developer (or just interested in application compatability on Windows Vista), you can also head over to MSDN's Windows Vista Developer Center for a wealth of resources on developing applications specifically for the new OS.