I have been using Windows Vista on my self built computer for over 2 months now without issue, vista even pointed out to me that I had bought a bad RAM chip.
Stability has been excellent, I have been running about 10 or so programs including Office 2007, adobe reader 8, and Windows media player, including a program called Folding@Home (which uses your processor to do Protein folding for scientific research) without issue for about 4 days straight now.
I also have Windows XP Pro installed and have not switched or gone back to XP except to check for updates.
A little about my system now.
I have a Asus M2n32 SLI deluxe Wireless Motherboard
(drivers on there website are still in beta)
Amd 4200+ FX2
2Gigs of DDR2 ram 800(do not get anything less then this, otherwise it sluggish and slow when opening programs)
X1300 Radeon graphics PCI-e 512MB graphics, Vista loves graphics and will utilize that.
Everything else is pretty stock, have not had any issues with drivers or programs, but I do not play games on mine. I have used Dreamweaver 8, Photoshop CS2, etc.
Oh and one other thing I have Vista Home Premium.