There are a lot of hostilities about changing to Vista for many reasons, but the biggest reasons it seems is issues with support for older or rarer software and hardware (including printers and other peripherals,) and changed settings and features. The core of Vista itself may be a good foundation for Microsoft to work from, but unfortunately the user shell needs more work still. They tried to mimic some of other OS options and features from Mac and Linux, such as the Aero visual themes, and User Authentication Control. With some more tweaking and changing to make these a little more friendly, they may have less resistance.
The biggest problem is that many of the people who really like Windows XP were upset with some of these semi-Mac type features that Microsoft used in Vista that seem uneccessary, buggy, or just plain stupid. Many are just going to wait it out until Windows 7 is (supposedly) released in a couple years. Unfortunately, from most of what I have seen and heard, Windows 7 will be little more than Window Vista with a few different features and support for multitouch interface. If this is so, then it will be a huge disappointment for the majority of Microsoft's customer base which is already mostly disappointed with Windows Vista and having a long difficult time transferring over. Still, that's all up for debate until Windows 7 is actually released.