Check out the "Mojave Experiment", where Microsoft brought in people to show them a un-released version of Windows.
Having been part of the Windows 95 team, and then shipped components in Windows 98, Windows 2000 and Windows Vista, I'm used to people complaining that the newest version of Windows is not as good at the previous version.
There are a lot of misconceptions about Windows Vista - that's it's slow, that feature X is not as good as it was in Windows XP, or any number of possible excuses. Many of the people doing the complaining haven't used Vista, or installed it on hardware that didn't meet have the recommended system requirements.
If you have Windows XP and are concerned that Windows Vista won't work with your hardware of existing applications, check out the very useful "Windows Vista Upgrade Advisor" tool.
What's your favorite Windows Vista feature? Of course, I'm partial to Speech Recognition and the Microsoft Anna TTS voice, but there are many new features, tell me yours.
Update: The New York Times collects some reaction.