DRM.
Try
copying some large files around and see the difference between XP & Vista
I'd estimate that it's between 1/6th & 1/10th the speed that winxp is.
You will find that vista is much quicker if you rarely shut it down & only use the hibernate & resume features of the laptop.
I personally, am eagerly awaiting the release of either Suse10.3 or Ubuntu/Kubuntu 7.04 which will hopefully correctly detect the sata controller & hence HD of my godawful dell laptop ......
I don't like that path that M$ is Heading.
To top it off, Vista Home limits the half-open TCP IP connections to 2 .. read T.W.O .. outgoing connections!
There was an uproar when XP SP2 limited it to 10 outgoing connections.
The reason being "We want to limit virus proliferation".
By my (admittedly quicky) calculations, at two PC's a second, a well written worm could still infect every PC in the world in approximately 30 seconds (one billion PC's)
The only valid reason they would do this is to hinder P2P activity.
Maybe that's why they also fubar'd the file copying/moving. No file sharing!