I've been running Linux on the desktop since 2002. I used Fedora until this past summer when I bought a Dell Ubuntu system. My wife, who is not computer literate, and my 8 year old daughter have neither one had any problems. Occasionally a relative will buy some kids game at Best Buy as a gift for my daughter; but we've made it through with Wine for the most part, though not always. Occasionally we hit a website that doesn't work in Firefox, but they're getting fewer and farther between. Now that Flash is giving respect to Linux, our experience is very pleasant. Even those glitches provide a better experience than we had previously running Windows.
I don't worry about viruses, and I have all my geek-tools at hand, while my wife and daughter do just fine creating docs, sending email, surfing webkinz, etc. I've not found anything that I really want to do that I can't because I'm not running Windows.
But perhaps the best part about it is that I don't feel like I'm having to pay Microsoft to use my own computer. It's my data; I shouldn't need to pay them to access it.