Some compatibility initiatives for Vista that I find interesting:

Application Compatibility Community : Gives you good description of the "Certified for Windows Vista" logo program and "Works with Windows Vista" is a compatibility designation.

Windows Quality Online Services (Winqual): Winqual enables you to qualify hardware devices, software applications, and Web services for Microsoft logo programs. This page has good data on: Windows Error Reporting (WER) and Crash Data, Driver Distribution Center (DDC) and Windows Update, Windows Logo Programs and Windows Product Listing Sites.