These are the approaches I've taken to try to convert them, and why they failed:
I had my mom running red hat 5 for a year or two; occasionally she would have a problem and page me. Once I did such an "urgent customer support" session at a pay phone in a cinema. The machine had the gnome desktop, and I fondly recall recalling my windows technical support training when I started every thing that she was supposed to do to fix her computer with the instruction "Click on the foot."
Telephone support based on gnome desktop was essentially the same as windows-95 telephone technical support.
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Yesterday morning I paid for a body shop repair on my van with my "linux fund" credit card, which is an MBNA charge card with a very cute tux on it. The clerk recognized "linux the penguin" and asked me what linux was, but glazed over when I tried to explain what an OS does.