Shoot - I'm running Vista Business on a seven year old Gateway (P4 1.8gz). The only three upgrades I did - increased the RAM to a gig, changed the video card to an ATi Radeon 9550 and the soundcard to a CreativeBlabs Audigy SE. Office 2007 runs faster under Vista than it did under WinXP, and Photoshop CS3 runs as fast.
Given the security that's built in, especially for laptops, I'm personally impressed with the efforts of Microsoft.
'course...it helped that both Vista Business and Office 2007 were free - I particpated in two Microsoft events and the above was the give away for my time (a whole four hours...)
