Share a single mouse and keyboard between multiple computers with different operating systems, each with its own display, without special hardware.
Synergy 2 is truly the best of things. It's free, open source, and is operating system agnostic. Which is to say that you can switch your keyboard and mouse across a Mac and a PC, or use your MAC's keyboard and mouse to type on your PC, and then flip back to the MAC in a quick flash.
In my case, I have a 12" netbook with an amazing keyboard, and when I want to do something on my desktop PC, like change the song on the playlist, or write this blog post while eased out and reclined on my couch, I can do that, thanks to Synergy.
Download link: http://synergy2.sourceforge.net/