Many of us have spent large amounts of time and money to build our computers. We take extra special care to route the wiring so the system that we have lovingly built gets maximum airflow throughout the case. The problem lies when we have no room or the case is just too big to get it up off of the floor. If that floor has carpet you can then run into some serious overheating problems with your power supply. The weight of your computer is often heavy enough that after a bit of time it will sink into the carpet and underlayment severely blocking air flow to your PSU. The pictures show how I took a simple piece of 1X8, drilled holes and added castors to allow ease of movement and great air flow for the PSU. I added some trim just for looks, as you can see I am no carpenter. It sure makes moving it out from the wall painless.
http://s1292.beta.photobucket.com/user/evo80ci/library/Computer%20Case%20Trolly