My Grandma has been running the debian stable line since 2006. I have not really had any issues that couldn't be solved. For the most part, depending on the sites/emails that she goes to, you will have to jump through hoops to get videos to play right/automatically. But it is possible. With facebook replacing email in the older generation (it seems), you might just get away with having only flash for videos. The other issues are getting pictures off of digital cameras. I wrote a quick script that can be ran when you plug in a camera and it will get any new photos and copy them to a special directory. It is smart enough to not download pics that are already there.
Surprisingly, when company has come over (it is grandma's house afterall), I have never notice anyone comment while they are using the linux computer. They just seem to all use it find. Never asking "What the heck is this?".
