I installed Linux Mint on my father's laptop last summer, after years of resentment "Linux? what's that, I need to use programs others use as well!". There was Vista preinstalled, but it seemed alienated to him and bloated (couldn't even connect to my wireless network), that he agreed to change it to "whatever". He uses it only for web, email and some office work (Firefox, Thunderbird and OO did the trick).
I had to leave early after the installation, so I didn't get much feedback, but I didn't hear any cry for help. In the holidays, he expressed gratitude, and "how can unorganized people make so good a system?", hehe. He looked skeptical, when I started to upgrade the machine, as he is used to Microsoft's shenanigans (New flashy GUIs he doesn't really need!). But after the update from 5 to 7 (was pretty hard though, should probably have done a 5-6-7 and ATI closed source driver isn't supported any longer), I changed the theme back, and he went on using it, as nothing has happened :)
Apparently he isn't a total non-techie, since he managed to installed some programs, since I have been away. And this was without showing him. But he didn't do any updates (I don't know why Mint uses a Lock as a update-symbol, it doesn't do the trick in my book (as a M.Sc. Interaction Designer and a study of visual design especially).
On a side note, I am pretty annoyed about Ubuntu's screwups of the audio system though! On my laptop (Mint), I need PCM at 90, so it would sound ok, but Pulseaudio puts it at 100 at every use (so I use alsamixer instead). On my mediacenter (Ubuntu minimal), the AUX is making a hissing noise, so I have to turn it off at every boot, since it doesn't save alsa settings (and since it is minimal installation, it is not even pulseaudio that screws up this time). Both issues has happen recently at an update, but I have read on google, that many more have had this for years ...