Very interesting ResleyZ, I have played with various kvm and vnc offerings that do things like that before but that looks like it will be many times simpler to pull off. I will have to try it out.
Edit. Tested it out (linux server with windows 8, vista and debian clients). Pretty painless, worked with multimonitor on my server, a bit laggy when wifi is involved but I expected as much being as far away as I am from the routers the devices were using.
Next step is seeing how it plays out with virtual machines, I do not imagine it is going to be too troublesome beyond the normal network stuff.
I might also consider a magic tablet of some form as well.
Definitely easier than messing around with something like TightVNC as a "third monitor".