Well for me Windows XP was something, that MS started but haven't finished. Since Windows 2003 was released I use it . I have Windows 2003 Enterprise Server Trial ( for 180 days ) so it's "quite legal" even :-). Earlier I used Windows 2000 Server also trial but NT 5.0 was really easy to damage :-/. But 5.1 ? Whoo - It can work days and days without reboot. I'm a home user so for me even a 3-4 days ( for eg. when downloading something all the time ) without reboot / BSOD / slowdowns / crashes / hangups is really something.
Besides NT 5.1 I used also Mandrake ( later Mandriva ) and Slackware. But it's really hard to let go those idiot-proof Windows wizards

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But what Im't trying to say : first leaked Longhorn BETA I've obtained ( don't remember when but I think that it was really the first first which was on the p2p ) was...kinda disapointing. We here have Gadu-Gadu. It's something like messenger or ICQ . But crappier. Anywhey every time I've launched GG - explorer crashed. Same with few other programs. I know - it was a BETA ( and still is ) but it was kinda funny that "wonderful new OS" can be beat up with GG

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I don't know if I swith to Vista. I really like Win2003. But I hope that software developers won't force us to use it...