Speaking from personal experience in migration battles with my wife:>

The reality is most non-tech "appliance operators" don't give a thought to what's in their computer. At least that's my home experience. The migration away from outlook to purely web based mail was not traumatic. Firefox replacing IE has been a recurrent headache. Largely born of UI changes breaking her learned interactions, I have had her use my oft mentioned Kiosk install of Puppy 4.0 with an amusing set of comments. Most notable being the frustrations over subtle differences,

That is going to be the headache inducing leitmotif for all migration projects if mine is any indication.