Macessity has announced the answer to these storage questions with a new line of products for the 2010 Mac minis. The MX4-V2 is a rack tray (above) that holds up to four Mac minis so you can "rack 'em and stack 'em" in any standard equipment rack. The $79.99 tray has special holes for cable management and comes with the necessary mounting screws (don't laugh -- you can never find mounting hardware when you need it).
For those who just want to hide a mini under a desk, there are two Macessity solutions: the $49.99 Mi360, which tucks your mini away in a protective compartment that rotates a full 360 degrees. It also has a theft deterrence locking tab so you can keep your mini from disappearing. If you want a four-port USB hub with your mini mount, you can get the $54.99 MiClassic (below) and add a $19.99 swivel bracket for convenience.