If you look at Windows XP from a stability standpoint, it has proved its worth many times. It has been around since 2001, so many companies have adopted it as the operating system that their network must function off of.
I have heard what Shane has said in numerous instances, being that many people are waiting for SP1 to be released before they trust Vista as being a viable alternative to their trusted XP OS (Listen to the Windows Weekly podcast on the TWiT network; they'll keep you updated

). Once SP1 is released, I think that many companies will realize that Vista
is the future and they do not need to rely on XP.