We do intensive software development on DELL M6300 laptops. They are heavy machines, but fast and reliable. I was on XP Pro, but just moved to Windows 7 64 bit.
I have used an endless series of Dells for years, only upgrading when I needed better performance. They are like refrigerators, in that they just run forever no matter how much you beat them up.
I've had several Dell desktops in the past and loved the upgradeability of them but don't dabble in hardware anymore and prefer to spend the extra cash to get all I need up front. So, I went with Dell and got a discount through my employer. My XPS, although it is still going after 3 1/2 years, runs consistently hot. So much so that the little rubber bumpers on the bottom would never stay glued and I had to rig up a makeshift stand to keep it off the table. I have heard from many folks that Dell laptops run hot. PLUS, my first battery died shortly after 1 year. Never had that happen before.
My neighbor's HD died while still under warranty.
Now, I realize that Dell is really just a box maker, as are all U.S. companies that sell computers and that all the inside parts each have their own manufacturer, many off-shore, but as eveidenced by my sig below, I think I am simply burned out altogether on PC's. I believe MS Office, that I might need for work work (if I get the job) also run on MAC's.