I have two machines, one is my laptop that I use for WPF development and other development work. It runs Vista and I can't say that I've ever had a problem with it, except when running games. I like a lot of new features of Vista and recommend it to people regularly.
My other machine is strictly a gaming machine and today I'm removing Vista from it. Why? Not because of some arcane reason, but because the Nvidia drivers for non-8000 series video cards are not stable. My laptop has a 7900 GS and when gaming, I get regular video driver restarts, which Vista handles quite beautifully, something XP couldn't do at all. However, these restarts are an annoyance at best and sometimes cause the game to crash, even if the OS doesn't go down.
On my gaming machine, I have SLI'd 7800 GTX cards (they were good when I bought them two years ago). They also seem to suffer from the same instability, and I've had it. I'd hoped the latest version of the driver (169.something) would solve the problem, but it didn't so I'm bailing on Vista until I get a new machine with a DX10 graphics card (or get a DX10 graphics card).
So sad, but oh well.