For what it's worth, I had the same experience with my parents. I installed Ubuntu on my dad's laptop and my mum's desktop. They loved it for quite a while - it was much faster, no security problems and no weird errors. I was so happy that I left a few comments online similar to yours.

A year or so later, they both use Mac. In both cases, the inevitable question came "so I bought this <peripheral/software>, how can I get it to work?".