It is becoming increasingly more common to see people using two towers with one keyboard, video and monitor. This is accomplished through the use of a KVM switch - as you probably already guessed, KVM standard for keyboard-video-mouse. This is great for people who need more computing power than they can get with one machine. A good example of this would be in a graphic design environment where you are consuming a high percentage of your available RAM and CPU power to run heavy editing applications.

For some people computing power is not a huge issue, but they could use more desktop space: enter the dual-screen setup. This allows you to have two monitors that essentially share your desktop. You can drag items from one monitor to another and if you have a long window you want to view, you can sprawl it out across both monitors. This is great when you need to use another screen as a reference or you want a static window that you can always check (with stock symbols, sales figures, etc.).