Multi-Point/Input Computer System

One computer supports multiple sets of keyboards, mice and monitors. Sounds cool. Just like 4 cursors on the Wii game screen. Why don't we make it widely available? (Well, then perhaps we don't need to buy that many computers because one computer can be used like two!) Imagine about these scenarios:

1. While I am working on my paper, my wife wants to check her email. I don't want to stop because I am all on it, but she does not want to turn the other computer on!
2. My friend and I are researching something online together. Constantly one person has to master the keyboard and mouse and the other person uses the finger to tough the screen. And constantly one of us will say "well, let me do it" and the other will reconcile the keyboard/mouse.
3. Playing games together - just like Wii (see http://mymousegames.com/ but it needs specially programming).

I think the current computing powers can achieve these tasks easily. PC makers just need to incorporate them in the hardware and software infrastructure.