I've got a Linux workstation as my primary box at work, and a Windows computer on my left side. So, I've got two keyboards and two mice and two monitors. I was looking for a way to switchbox my keyboard and mouse. Ended up finding x2vnc.
Now, I move my mouse to whatever edge I designate, and it starts sending my mouse and keyboard output to my windows computer (with a listening VNC session). Very slick and very useful.