I switched my father from Windows XP to linux several years (7?) back because it was easier for me to support at the time. I would not rate it a success and he has since switched to a MAC (which is also a failure but that's another story).
Just some of the reasons:
1. Lack of a reasonable Email client that compares to Outlook.
2. Support for scanning documents is horrible. Assuming you can even find a scanner that works, there is no good scanning software on Linux.
3. OpenOffice documents are not 100% compatible with Office (though arguably, Office versions are also not compatible with each other so that may not be fair).
3. And most importantly, lack of support. My father uses his computer for his consulting business and I work full time. I can't support him during business hours and there is no place else to go. You can't just walk into Staples with your laptop and ask for help.
There were lots of other frustrations over the years that I've blocked out of my memory.
If you're just doing basic stuff like web browsing, then _maybe_ Linux would work for you but you have to live with a lot of limitations related to browser incompatibility, plugins etc. For example, will you're banking site work?
I said it in the other thread, for basic use I'd go with an Android tablet hands-down. It requires minimal if any hands-on support, and it's also very well supported out on the web with apps for pretty much everything. And you can't beat the price.
John