Ubuntu (and Mandrake or Suse) is nice if you have fairly standard hardware. However, with anything esoteric, it can be very frustrating. I've got a Canon network printer/scanner, a satellite card and a DTT card, plus an AV input device,which either have no Linux drivers or if they do, they do not have the same functionality as windows drivers.
Windows 7 RC seems very good - it just works. Even cosmetic features like desktop wallpaper transitions are gorgeously slick.
John