I've been using Vista since early January (pre-release copy). I received my copy free through Microsoft's "Power Together" program last year.
At first, I wasn't too keen on it. The drivers for my hardware were quite immature and apps seemed to run slower. Mind you, this IS before any patches and updates were released.
But for the past 4-5 months, I've used Vista as almost my exclusive OS. All my apps and games work excellently (I'm a big gamer, so this is important), stability is improved over XP, and my wireless network and internet is actually faster and more reliable under Vista. Granted, this is probably a function of the drivers for my router being better for Vista, but it just goes to show that hardware drivers ARE maturing quite nicely, and in some cases, things are working better in Vista.
I still dual-boot XP Pro and Vista, just in case I DO encounter any issues that have yet to be resolved.
But so far I've not found that to be the case with my setup.