Here's another vote for win2k over winxp. I just spent the day installing xp pro on my girlfriend's computer and I found it to be quite annoying at times. And my god the interface is terrible -- even after turning everything back to "classic" windows, microsoft has hidden many advanced settings and adjusting them can be very counter-intuitive. I found trying to adjust NTFS file security settings to be quite confusing, for example--unlike the very intuitive win2k interface. And I couldn't believe it--after setting up two users during the install, winxp made them administrators but didn't assign them passwords or ask to set up a password! What a totally dumb default setting and a huge security hole for corporate settings (this is winxp pro after all....) I have dozens of other minor (and not so minor) complaints about xp as well but they have all been discussed here at length. I get the feeling that xp could have been a much better product than it is, but that some very bad decisions were forced on the development team for some weird reason(s). As it stands, I suspect that more technically minded users who have used win2k in the past will prefer it to winxp. The only good things I could see about xp was the amazingly fast boot time (about 30 seconds by my count) and of course the stability offered by the NT kernal. But I'll stick with win2k for my microsoft computing for quite some time, thanks very much.
Oh, and product activation and .net nag screens are at best really annoying and at worst demonstrate a total disrespect for MS customers IMO, but I won't even get into that here...