@bertino
OK - my experience with randomly bought stuff of my own or belonging to other family and freinds:
* Printer
Some do work, with a lot of effort, but many of the cheaper ones rely on Windows drivers and so will never work properly under Linux - if at all.
* Scanner
Do you really think that most people buy network-attached scanners? These days USB ones are cheap, cheerful and good enough for 99.9% of home use. Unless you expect to find one that works under Linux.
* DSL modem / router
Several ones that I have bought recently come with a CD-ROM that you insert into your PC to set them up. This runs a wizard that goes through all the required items. Windows only of course! Sure, they are not the best kinds of routers, but your granny will buy the one that the guy in Dixons or Walmart offers, not the one that got 5 stars in last month's Linux User Monthly.
* Digital Camera
Generally you can get these to work under Linux, but the CD-ROM full of goodies is basically just a coaster. Which is sad when some cameras come with loads of interesting and useful extras.
* Digital Video Camera
Yes and no. Again, you may be able to get the videos off and play them, but the supplied video editing software and the tool that automatically uploads your stuff to YouTube won't work!
* MP3 player
Chances are, most average users want an iPod. And iTunes. Oops! You may not rate these, but there is a reason Apple have stacks of money!
* Smartphone
My smartphone only came with Windows software. I know of several others that are tied to Windows and/or OSX.
"Which means hand editing config files. Or changing boot parameters so that you get something other than a black screen etc. I would like to say that once fixed in linux it stayed fixed, but this is not the case anymore. The EEPC901 wifi driver needs to be recompiled from source with every new kernel for instance"
Ah - now that sounds like the sort of stuff I end up having to do to get peoples machines running Linux - and trying to talk the mother-in-law through that over the phone when something goes wrong is not exactly fun!