Except for a limited number of niche users, there's really no need to use Vista. DX10 might be one of them, but even the games that use it still mostly support 9. If you like the eyecandy of Aero, go to youtube and look at Compiz Fusion. If you're still impressed by Aero, then I'll never change your mind. Security, there's nothing Vista has that can't be done on XP with free 3rd party programs, and that goes for pretty much all of the other "features". Sure, the average user can be perfectly happy with Vista, but they can be just as happy for cheaper with XP. Or you can be happier still and learn Linux. It's not nearly as hard as most people think, and except for a slightly larger niche group, will do everything you need.
Vista Home Premium on Newegg is $100, XP Home is also $100, that's not cheaper with XP.
Stuff that can't be done in XP with free 3rd party programs:
- Support for large amounts of memory
- Improved memory management
- Improved multi-core management
- Improved audio stack
- Improved update system
- Increased performance
- Improved networking
- Improved driver model