As far as the OS goes, WinXP has its good points. It has almost more built-in hardware support, bluetooth, wireless internet, drivers, which make it much less of a hassle to install. Don't get me wrong I don't mind going through and installing each driver individually, but you gotta like the fact that XP has most of them included. Not that your installing the OS everyday.
From day to day usage I find XP to be faster than when I had Win2k. Mainly because XP supports hyperthreading and Win2k doesn't. WinXP's built in support for bluetooth and wirless is better than many of the 3rd party apps. The new GUI is nice and I've gotten used to it. I used to swear by the Win2k look, but now I like the WinXP look better.
Yeah XP might be slower because of all the GUI enchanments. However if you turn these off and go back to the classic theme it is the same as Win2k if not faster, due to better hardware support.