XP Mode is nasty
XP mode is a horrible, horrible cludge. There are much more elegant virtualisation solutions out there. It seems to me that the only real benefit of XP Mode is the officially licensed XP within.
What many seem to have missed is that a lot of European enthusiasts who are privately upgrading to Windows 7 will get the full version rather than the upgrade thanks to the EU shenanigans. If their previous XP installation was also a retail purchase this means they will end up with a 'spare' XP license once they've installed 7. My advice is to install Sun VirtualBox on your new Windows 7, set up a virtual machine, and run your old licensed XP on that in 'seamless' mode. I've used this method and the official XP Mode and there's no comparison. The former is so much faster and easier to administer. And VirtualBox doesn't require hardware VT.
The same will apply to some new hardware purchases. If your new machine comes with Windows 7 and your previous XP was retail, you have a valid XP license to use in any VM package you like. You don't need Microsoft's 'solution'.
For anyone who doesn't fall into any of these categories, now might be the time to shop around for a cheap second-user retail XP. If your only reason for choosing Windows 7 Professional is the XP Mode and you can obtain a cheap enough XP, you may well find it more economical to buy Windows 7 Home Premium -- or a new machine preinstalled with the same -- and a separate XP to run on VirtualBox.
It's only a pity you can't legally use OEM XP on VMs, or there would be an even cheaper solution.