The placement of the magnet should be centered (left to right) just above the USB connection, and about 1-1/4" up from the bottom. To clarify - placement of the magnet does NOT distinguish car mode and multimedia mode. The polarity of the magnet does this. Hold the magnet onto the back of your phone (location I stated) and see which mode comes up. Flip it over to see the opposite mode.
The magnet will help hold the Droid in position if you have it completely vertical. Best to lay it at an angle though - you don't want it falling off, and the magnet is not that strong. Especially if you have a case on it. Our MIKRADLES use a 45 degree angle to support the Droid, which is a good viewing angle when placed at normal desk height.
I must commend all of you for the very innovative use of your Legos!
cuskit (inventor of the MIKRADLE)