Would you like Windows or Linux as your OS, Why not both?
Since the advent of Vista, I have been offering the choice of OS on systems I build.
Occasionally I get asked to do a dual-boot system, and about 50% of the time I've had it back to wipe the windows partition, and, it must be said, 10 to 15% ask to have linux removed in favour of windows. Usually because they have bought an el-cheapo windows only printer, occasionally because their boss has insisted that their system be Windows, or we can't find a linux equivalent for a windows program that they do need, usually Quickbooks or MYOB.
The pricing of the systems reflect that I can download a copy of, usually, LinuxMint in about 15 minutes and burn it to a dvd and that the setup is far quicker than for Windows.
Windows is still leading the install rate at roughly 80%, because that's what people are used to.