So far all I've used it for is to control a train so that I can start and stop it with a button, next I need to add sensors on the track so that I can have an automated train.
These pictures are taken with a video camera so sorry about the fuzziness.
Here it is with the side off.
With the side on, a 14x6 plate instead of the standard doors.
And here is a shot of the end showing the transparent red bricks
that allow IR communication without removing the RCX.