First I need to say that I love Synergy. I have used it at work and at home for about a year now and I use it constantly.
For those who are not familiar with Synergy, it is a utility that will share a keyboard and mouse with multiple computers over your network. So, for example, I have a Windows XP system and a Ubuntu system, both with their own monitors, with Synergy I can use the same keyboard and mouse on both systems. This cuts down on the need to have multiple keyboards and mice, and is obviously cheaper than a KVM switch.
When setting Synergy up you will select a side of your monitor on each system that is connected between both. So you can drag your mouse across the screen from one computer to the next. Kind of like having multiple monitors but between systems instead.
The Synergy website has good instructions on setting Synergy up here. Also Synergy will run on Windows, Linux, Unix, and Mac OS X.
I was a little worried when I noticed that Synergy has not had a release since April 2, 2006, but I did a little digging and noticed that there have been SVN commits since then and in a forum posting the lead developer stated that he has been working on version 2.0 and hopes to have a alpha/beta release around March.
Here are a few helpful or informative links regarding Synergy: