They've got the worst bugs out of XP, which is a stable, versatile and (with a little care) reasonably safe OS. They're only just starting with Vista which won't be RTM for 6-8 months (and rapidly followed by a huge "service pack").
Apart from gorgeous eye-candy (for high-end systems only) Vista isn't doing anything magical that XP (or Linux) can't do. There's no "killer app" on the horizon or is there likely to be.
A 64-bit OS isn't magical, there are already plenty of stable 64-bit 'nixes and it won't make any speed difference to standard apps.
Device driver support, esp. for legacy devices is a big headache for Vista - many older devices will never be usable.
And the DRM!!!
By the time Vista is sorted out enought to be viable, in a a few years time, there'll be a choice of Linuxes that'll do everything that Vista does (including eye-candy), as or more easily, without the DRM, the "phoning home" and the not inconsiderable expense! And they'll run most MS apps (under WINE).
If I was to buy a new Windows machine today (unlikely), I'd make sure it was "Vista capable", but install XP SP2.
