Most of the PCs in the school where I work are Dell. Never had a problem with the desktops, and the few problems we've had with the laptops (which aren't treated that well!) have been sorted out next day.
if you buy from dell take out the extended warinty, great systems, but the warinty give you piece of mind my system nearly 2 yrs old had problum with dvd r/w in less than 2 days engineer there and repaced it with new
the only annoying snag is that now (i think anyway), they don't come with the operating system discs, and instead use a restore partition. personally i disagree with this. but anyway, lots of companies are doing this now (HP, compaq, etc.)