I build 3D Multiseat
Multiseat - a system with one case and several graphics cards, monitors, keyboards and mouses. Allows multiple users to work simultaneously with one computer.
In the configuration described 2 user can play 3D games DirectX9 using wine-1.0, for example, Heroes of Might and Magic 5 (HMM5), WarHammer 40k (WH40k), Serious Sam 2 and others are not impeding each other. The system easily expands to 4 seats.
However running Wine/Cedega/Crossover you don't have as good a library as the Windows system it was designed for.
I can already see applications for lan parties or even for game / internet cafes. "I don't have that good of a computer." "Bring your USB keyboard, USB mouse, and a monitor and hook into mine then."
I wonder how para-virtualization (Xen, VMWare) can be applied to this. It would probably be able to protect the other people if someone's X server crashes.
It could probably also use a "System Diagnostic" screen, maybe remotely or out to the TV, to be able to fix or update on the fly.
One X server crashes does not influence others !
You can even press Alt+Ctrl+Backspace and gdm restarts a server, other users at all will not feel anything. One crashed the server borrows only one core of the processor. It is checked up.