Well, my dear old Dad at 79 is coping fine with Linux and he's quite the computerphobe (he curls into a ball at the drop of a hat with new things). His needs are fairly basic - word processing, spreadsheet, e-mail, browsing and a few games. I ran him through things over several days and he hasn't looked back at WinXP once.
I did ease the way by making sure over the last few years that he was using programs that had Linux versions (OpenOffice, Firefox, Thunderbird) so the transition wasn't complicated by learning a new program as well.
He needs a bit of assistance for time to time or forgets how to do things, but then he did that with Windows too and it's not really any more frequent.