This comes from Philip Elder's blog:

When it comes to moving systems around, it is important to let users know that they need to keep contact with a metal component on the CPU tower before and during any moves taking place.

The system should be properly powered down before removing any cables from the back of the tower.

Once the machines are powered down, it is important to make sure to remain in contact with that metal while removing the VGA, DVI, USB, and network cables.

The A/C cables should be the last things to be removed from both the CPU tower and monitors. Make sure to use the power switch to turn off the power supply if one is present before pulling the plug.

The reverse order should be used to connect everything back together all the while making sure to be grounded during the process.