I don't feel like writing a diatribe just to get my opinion thrown back at me accompanied by some silly metaphor that doesn't really fit the situation, so I'm just going to point out a single thing (out of many).
Microsoft does not put enough effort into their user interfaces to make them truly user-friendly and easy to use.
That's right. Vista represents a patched together mess of amazing, dazzling new graphics and random visual effects that are thrown around the interface in a way that it seems Microsoft is trying to cram as many cool effects in as they can...just so they can say "we have a cool interface with moving effects and stuff." It doesn't matter simply that Vista has Aero, has some fancy effects in applications, has some "gadgets" over on the right of the desktop if it isn't designed and implemented well. You can't throw together a bunch of features without meshing them together in a seemless fashion and expect to end up with a good product. However, Microsoft's software development strategy has done just that. With Vista it feels to me like Microsoft has taken XP, created a long list of neat things that should be in there, narrowed it down (a lot), and then assigned a single individual task or feature to a separate developer. Then, when the work is done by each developer, it is all compiled into a new operating system and, ta da, you've got Vista. NOTHING MESHES. Everything is separate, like the pieces of 100 different cloud puzzles thrown together to create a single picture. You've got something whole, yeah, and it might work...but it doesn't flow together. Everything is disjointed, and the easy work flow from third-party application to built-in feature to etc etc just doesn't exist.
That's one reason I don't like Vista. I could write many more, I'm sure, but you'd end up reading quite a bit. Take it as you will, and I'll stick with XP until UGS NX5 and SolidWorks are converted for native Mac use.