get off XP, its nearly 7 years old and its time has come.
What you are forgetting here is that an overwhelming amout of business applications will not work with Vista. An overwhelming amount of hardware will not work with Vista. It's sad that vendors delayed being ready for it. There was more than ample time for them to prepare.
In a large business organization you are not going to see management spend the money for this either.
A) The training involved with a large amount of employees would cost quite a bit and cause a drastic loss in productivity. Support costs would also increase.

The hardware costs.. nuff said there.
I work for one of the top IT Outsourcing companies in the world, supporting IT for a very large healthcare organization which owns approx 130 Hospitals throughout the US. You can't imagine how behind the software companies are and the costs associated with upgrading in this industry. Windows 2000 is still quite strong here.
At least the Enterprise Licensing for Vista is backwards compatible and will allow us to continue installing XP on new systems.