I have XP around but I haven't used it much at all for at least three years now at home. Both machines I use daily are currently running Ubuntu. The only thing I really need Windows XP for now is my scanner which unfortunately Linux doesn't support (Epson is notorious for lack of Linux support). Personally Open Office does everything I want and a whole lot more so I have never missed MS Office though I have Office 2000 on an XP machine. Gnucash looks old fashioned and also very 'QuickBook's basically to be easily picked up and handles private/small business accounts very adequately. Scribus copes with my modest DTP requirements fine and so on. None of which costs a penny.
The comment about changing an OS with the computer is very valid but what about the anti virus software, office software and so on needed? I suspect quite often people are already using open source/free alternatives. It was those costs in large part that initially got me interested in Linux. My mothers laptop is running XPHome but in fact everything she uses is opensource/freeware (Firefox, Thunderbird, Open Office, Picassa for her photos, Skpe very occasionally and AVG free for anti-virus.) She's been told, and doesn't mind the idea, that when XP dies it's getting replaced with Linux.
Oh and they wouldn't need to change hardware so often perhaps. (Just put Puppy Linux plus Open Office on an 8 year old laptop and the owner is very happy with the result. Wouldn't run Win2000 at more than snails pace and I gave up trying to find drivers for Win98 that would work. The desktop I use most is a 1200Hmz Duron with newer but basic FX5200 graphics card and pretty responsive even running Ubuntu with mid level eye candy settings on. Given it has ample RAM I suspect it will do decent service for a couple of years yet unless the MB fails.)
I've persuaded the little charity I support to put Ubuntu on its laptop and no one has complained about it though a number of people use it. Most of the software apart from the OS they use on the other machines is opensource/freeware so the applications are the same. They even generally find the server without prompting fine. They are obviously basically unconcerned what the machines run as long as it works and they get their work done. They're quite happy with the idea that when the XP machines die they get Linux rather than a reinstall of XP. (Helps they have legitimate copies but have long since lost the discs and license numbers and I haven't mentioned I can recover the license number from the machine if I want to and do a legal reinstall via that

)
Richard.