There is nothing more ergonomically and functionally annoying than to have to use two machines sitting next to each other, and having to switch between keyboards and mice to control them. Inevitably you forget for a second, and try to move the cursor or type on one machine with the mouse or keyboard for the other machine.
The perfect solution is to use a single mouse and keyboard to control the environment of both machines as if they were a dual-screened single system (i.e. moving off of one screen transitions the mouse and keyboard focus to the other screen). Over the years many solutions have been developed and adapted. Hardware solutions (KVMs) can be expensive, so software is often easier to implement on a budget. One piece of software most Unix-types are already familiar with is x2vnc. While x2vnc is quite nice and functional, it lacks flexibility, and ease of use for the average user. I recently came across Synergy, a much faster, multi-platform (Windows 95 through XP, Mac OS X, and Unix…including Linux) application that allows one to share keyboard and mouse between multiple machines (you aren’t limited to just two) with incredible ease.
I am currently using Synergy between a Gentoo Linux box and a Windows XP machine at work, and I cannot tell the difference between this setup, and the previous dual-screen, single system setup I was using on my Windows system previously. It’s that fast!