Ed Bott, our good friend over at Zdnet.com, has a great article on comparing feature changes between Windows XP and the upcoming Windows 7. He says, and I agree with Ed, that Windows XP users will initially struggle with Windows 7 new UI features, but should give it some time to appreciate the productivity gains:
The real problem most XP users will have when migrating to the Windows 7 interface is that they need to unlearn those old navigation models. The longer you’ve been using PCs, the more likely you are to reflexively assume that the solution is to pull down a menu or double-click an icon. Those techniques worked fine back in the 1990s, but today, with instant search available just about everywhere in the Windows UI, those old techniques are as dated as a pair of Dockers.