Some of us still work on Windows XP.
I myself still prefer to have my P4 3 GhZ Single Core at work to run with the "old" Windows, because of Ressources and the good feeling to have an proven system installed. The only thing that I find really annoying is the taskbar: I really love the feature of Windows 7 to reorder taskbar entries without restarting applications.
And thats something Windows XP can do as well with Taskbar++
( http://www.chip.de/downloads/Taskbar_19900036.html )

Just install and run it, move your mouse cursor over the taskbar and press and hold ALT.
The mouse cursor will change to a finger, then you can click and hold an entry and move it on the taskbar.
Let go of the icon and ALT and everythings set again.