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.

Your country mandate digital signature that aren't cross platform?

"Cross platform" is in the eye of the beholder.

How easy is it to use for someone that thinks their browser IS the internet to install and use?

Browser extensions?

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.

If you are a medium-advanced user with Excel it's not gonna be good with calc.

Linux is only going to be smooth for very basic stuff or if you have de knowledge to troubleshoot it.

You mean your parents can use your gentoo computer, or that you installed gentoo for them ? The latter sounds quite unorthodox.

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.

Similar history here with another distro.