Yeah same experience here. Installed gentoo on our home computer for my mom and dad and once i showed them how to open Firefox, they were happy as clams. The only issue was when my dad wanted to install tax software
Basically, they'll be okay as long as they only use the browser.
When they need to edit a MS Excel file, or use their digital signature (mandatory for companies in my country), or use some accounting software... or anything like this, you understand that Linux isn't as ready for the mainstream desktop as we think it is.
Some are compatible, some aren't. And even if yours is technically compatible, if you run into problems with the website or program where you need to use it -- and you will -- you're on your own.
My dad was happy with OpenOffice.org Calc (now LibreOffice), and he loved excel. But, yeah, obviously Linux doesn't run accounting or signature software that is not built for it. That's not a technical issue with Linux of course (see Android), but a lack of proprietary software that runs on GNU/Linux.
I installed it for them. It was more than a decade ago, and I chose gentoo because it was one of the first distributions to support amd64. Chose gentoo over debian because it had newer kernel versions that I needed for that particular computer.
When they need to edit a MS Excel file, or use their digital signature (mandatory for companies in my country), or use some accounting software... or anything like this, you understand that Linux isn't as ready for the mainstream desktop as we think it is.