I have a quadruple boot now on my desktop (osx/linux/xp/vista)
XP wins by far. The hardware is by no means brand new, but it is speedy enough.
Vista has a bunch of problems. Legit problems.
To name a few:
The endless reboot patch where it would destroy the kernel file when you install the update as a pre-req for installing SP1.
ACPI drivers (Microsoft side) are flaky at best. Dont know what they did, but there are numerous reports of S3 problems. Most are crashing on wake, but my laptop has a problem where I cannot put it to sleep if it is on mains power. I have to unplug it before I put it to sleep or the screen would turn off and never come back with the fans on full blast and HDD light going crazy. Left in that state it will run forever (at least overnight). And no I am not retarded and I know about the Power Options...
So much damned "protection" that it freezes windows mobile 6 devices over activation if you sync it with a non-Vista PC as well.
Dont know if they fixed this one or not, but if you had Windows Media Player open (or any program that can play protected content) while doing some update you would lose the ability to play
all DRM content... In all programs...
Again the stupid people protection now makes file copy so slow. It has to gain access to every file so you dont overwrite something valueable like the "windows experience index" xml file

and then ask for permission to copy them. Copying a single large file is not too much of a problem. But trying to copy a bunch of little files. results in doom.
Also the Out of Memory Exception is a particular annoyance that plagues me personally on my laptop. WHen trying to copy a large file between disks like from a CD to the HD or from HD to a flash drive over like 200Mb, it results in a huge system slow down, RAM goes to 100%, CPU goes to 100%, and after a while it comes back "Out of Memory" and cancels the transfer. This one has even stumped Microsoft because their tech files even say "we know it is a problem, we dont know how to fix it". So when doing large file transfers I have to open the command prompt and copy it that way with switches so it doesnt do the network check...
Should I go on?
So dont defend something you don't know about. People say Vista is crap, because it is crap. It looks pretty though.
