Well i am the odd one out here, as Vista just hasn't caused any problems for me, infact, its less troublesome that XP Pro.
The only bad thing i have noticed, or the only performance problems are, i loose a few frames per second from FSX, and the 3DMark score is a little lower.
Graphics are great though, getting well over 30Fps with sliders on tops and a few checks here and there. Video encoding is quicker and all that.
Oh, bad point, VMWare doesnt run as smooth as Vista hogs 256mb more RAM than XP on average, even then i am left with a good 450mb on average free, i used to like VMWare to have 512 but i can make do with 256.
I think issues are with under spec machines.
Minimum spec is what vista will run on, anything under that and vista prob wont run, so thats nothing to go on.
The recommended specs are more realistic, but i recon you need to double the ram and double the GFX Memory. So 1GB RAM and 128 Dedicated Memory would run it nice.
Dell are only moaning as they are getting more calls due to the fact vista just aint designed to be put on a machine with 256RAM, No dedicated graphics and Celeron.