Yesterday I used Windows XP Professional for the first time. It was an interesting experience. Comparing it to Windows NT4 and Windows 2000, I think it's a retrograde step with regard user experience. The first think you see is a multi-coloured "Teletubbies" or "Fisher Price" interface, which while it may be okay for four year olds, it shouldn't be the default for the professional version.
I turned all the annoying things off: animated menus; web views revert to classic appearance. After 10 minues of huntinga and killing, it almost looks like Windows 2000. The interface is still too busy, but now it's almost usable.
At home I use Linux running KDE, I've not run Windows at home for over a year now. Compared to Linux, Windows XP is busy looking, buggy and lacking in features. Other than games and viruses I can't see any advantages in Windows.