I've already told my customers - all of whom use XP - that they need to plan for an upgrade somewhere between 12-18 months from now. Working out the budget, testing, discovery of likely issues etc will all take time, and they need to do it before switching over becomes critical.
Eventually XP will be as easy to support as Win98 is now - which is to say, a total pain - and IMO anyone advising their customers that they never need to upgrade is misrepresenting their interests.
