I brought all of my computers in to work the other day so that I could be more productive. It's not like productivity is linearly proportional to the number of computer you have but having at least two computers helps. Disadvantage: switching between the screens takes time and a bit of effort. Advantage: the time it takes to switch screens is offset by the comfort of having machines dedicated to a single set of tasks so that you don't have to keep alt+tab back and forth.

For example: all coding is done on my main work machine (the T40 in the center). Viewing web pages (which includes viewing test pages and such) and MSDN is handled by my own T40 (to the right). My old Dell (to the left) handles AIM and Windows Messenger, and downloading some anime ;)

The Cisco IP Phone and headset to the left there is a godsend...call anyone and everyone and have your hands free to code and test things! Not a new technology but good nonetheless. You'll notice my own Astrotrain and wireless keyboard/moues there. Requisitioning things are slow and I've gotten the wrong items (how do I know it's wrong if there's no picture/description of the item I'm ordering?!) so might as well go with my own. Plus it's all fancy schmancy wireless (not that I need that capability).