Just out of curiosity, HN seems like a good place to ask: Does anyone actually here use unix-likes in a multiseat fashion, like they were used 30-40 years ago? Like described here:
https://en.wikipedia.org/wiki/Multiseat_configuration
Five years ago my wife and I shared an Ubuntu desktop. It was awesome, and we were even able to play 3D games together.
If I remember correctly, I had to bump the computer up to 6GB of RAM. She was running off the motherboard's built-in video card and I had two monitors on a separate card.
Eventually Ubuntu changed things so that it wouldn't work anymore, but I believe that it's possible to do now. If you have kids this would be a cheap way to give them all a decent amount of computing power.
In Finland, a number of schools nowadays use Linux in this fashion. This solution has been especially great for modernizing entire computer classrooms at once, recycling old desktop PCs as LTSP clients. A server capable of serving a classroom full of clients is a lot cheaper than replacing the PCs. In my town, there's a company called Opinsys (http://www.opinsys.fi/en/) who does this and publishes most if not all of their code in Github (https://github.com/opinsys/). I wonder if they've been considering Raspberry Pis as clients.
Yes, I have been using Fedora this way for a couple years now (ever since systemd made this easy in Fedora 17). Two heads, one running MythTV (most of the time), the other is my workstation.
http://www.x.org/wiki/Development/Documentation/Multiseat/
And if you're on arch linux this is a good start:
https://wiki.archlinux.org/index.php/xorg_multiseat