Windows Vista is here, sort of. Vendors are offering "Express Upgades" for systems bought today, which can be redeemed in February.
I do not like putting my clients on the bleeding edge of new operating system releases. As always, I recommend waiting as long as possible before deploying new versions. Let someone else round off the sharp edges.
Clients should consider that it will become increasingly difficult to purchase new systems with Windows XP. If you need new systems in the near future, buy them now with XP installed and with the Vista Express Upgrade. Then you can upgrade to Vista at your leisure.