If you have 2 computers that you would like to control with just one mouse and keyboard (and without a KVM switch), then check out this application. It uses a VNC server on one machine and automatically connects and switches all mouse and keyboard actions to that computer from the one your keyboard/mouse are automatically connected to.

The program will open a small (one pixel wide) window on the edge of your screen. Moving the pointer into this window will trigger the program to take over your mouse and send mouse movements and keystrokes though the RFB protocol to a VNC server running on another machine. When the pointer is moved back towards the opposite edge on the other screen, the mouse is returned to your primary display.

Pretty nice little application. I was actually discussing something like this with someone at the office the other day.