In the past. But now, MS desktop deteriorates and that process will only grow with Linux finally getting more traction. Valve's push for Linux gaming is one of key factors which will reduce MS grip on the desktop.
My wife uses windows because I can't convince her that google docs or openoffice are ok. She just prefers MS Office.
Valve's push may get us better graphic card drivers, but I don't know anyone who uses windows over linux because of that (I know a few people who stubbornly use linux notwithstanding crappy drivers though)
Granted, I'm not a good representative of the average user.
That's why it kind of surprises me that MS sticks its neck out on UX redesigns like the ribbon or eliminating the desktop, since every change gives the core userbase another excuse to try something new. (Even if there are a few good underlying UX ideas, like larger buttons, more prominent placement of common commands, and saving me a Win key before I just start typing to search...)
Depends on what you are using them for. I've tried to convince a lot of people that that is the case, and then I wrote a book and found out it isn't actually the case. They are good enough for casual use, they aren't actually good enough for more serious work. Editing in particular is far far superior with Word.