We recently bought a hand-full of DELL PCs for a development project at work that I'm managing and boy are they slow.
I know DELL gets bad press because they're pretty non-upgradable unless you buy the 'DELL-variety' of card you're looking for but that didn't bother me. What concerned me was the fact that my 1.5 Ghz PC was checking out code from the CVS server in seconds, whereas my colleagues took about half an hour on their 'super-fast' shiny new DELLs (2-3 Ghz I think).
Turns out, DELL install all these n00b-filters like McCrappy virus scanner and the Google processor-hog/search toolbar. That means that whenever you run a shell command it has to virus-scan the .exe file (even though it's the same damn one you ran several milliseconds ago) and each file you add or remove has to be (presumably) indexed by the Google desktop software. I never run anti-virus scanners in the background because most of them are pretty dumb and just kill performance.
Scanning through the program list looking for other stuff I could remove, there was all sorts of crap that nobody in their right mind would want installed on a laptop - why the hell does DELL think people want their 3Ghz PC to run like a 486?
This is why I buy the parts and install my own O/S and apps myself - I'm not paying for someone to 'dumb-down' my PC with stupid features that I don't need, save that crap for AOL users.