It's the speed of Vista that makes it frustrating for me - I've got a decent Dell Vostro at home (scores of 5.9 all the way on Vista performance index - quad core, 4Gb, etc) but it still doesn't feel responsive. It's not that it's slow, but compared to OS X or XP it's sluggish.
It's actually better under boot camp on my Macbook Pro, but that's using Vista Business not Home Premium so maybe that helps.
In truth, I'd find it hard to justify Vista to our schools am glad Becta have taken the stance they have with it, I just don't see Vista as an upgrade.