Easily using two computers with one monitor (not simultaneously) is easy if you're using DVI or VGA as your connectors, but if you have Macs with Mini DisplayPorts, you'll have to pick up a SnapX from Kanex. It works the same as most other KVMs, except it has a USB and a MDP for each computer.
This $US70 adaptor has 1.2m cables, and lets you use the webcam, USB ports and speakers from your Cinema Display on each computer, and switches between machines with the giant button on top. If you plug your mouse and keyboard into the display's USB ports, you can even have those switch along with everything else as well. Preorder starts now for September shipping.