After purchasing 25 Dimensions from Dell, and having the hard drives fail on each and every one of them, I standardized my office on Optimex systems. Truthfully, the reason I chose dell is that ever since the Gateway 2000 machines, I have been using Dell. Additionally, all of our servers are Dell, and our software was designed for Dell (it is only supported on Dells).
I haven't had great experiences with Dell in terms of customer service, but when something went wrong, they did send out someone to fix it. They even let me keep the dead Hard Drives to have them shredded.
We do use Sony Viao laptops- the tiny tiny ones, I don't remember what they are called, but they are excellent.
Generally, I am satisfied with the quality of Dells, though I have noticed a decline in quality over the years.