We wanted to put a radio controlled 1KW Triac based dimmer on a 1.5" x 2.5" board and stuff it into to a wall light switch box. I can almost do this on a single board. However, the switches, lights, antenna, and through-hole components made that pretty difficult so I decided on a two board solution that 'sandwiches' together. I do believe that we could (and will) reduce it to a single board in the future. Notice that the top board has very little on the top surface and the bottom board has very little on the bottom surface. If I used smaller parts (like 0402s) and all surface mount parts (instead of the big through-hole electrolytics) then I would have a chance of getting this all on one board. One big problem, however, is to find free space for the antenna. Ideally, the antenna would have nothing behind/under it. Even in the two board design, notice that the input filter of the power supply is behind the antenna. Only experimenting will tell if this is going to work.

The two boards are split into high voltage and low voltage parts. The high voltage stuff (Triac, power supply and sensors) are on the bottom board. The UI, logic and radio are on the top board. I have the boards constructed as one board. They are spaced by 200mils which is about the width of the blade on my chop saw. I plan on cutting the boards in half and having Abdul at Schipper's and Crew mount the CPU. I will then construct the boards myself.

The bottom board is meant to be lifted straight up and then placed on the top board (as seen in the images below). The bottom board (the high voltage board) is then meant to be the back-facing board and the top board is meant to be the front-facing board (that is why the components on the top board are on the bottom layer). The 8 indictor LEDs are meant to be mounted on the left. The three mode switches are meant to be mounted on the bottom of the switch as you face it mounted in the wall.

Here is the schematic.
Here is the Bill of Materials (OpenOffice Calc format).

All Layers. Here is an images of both boards with both the top and bottom layers enabled.
Top Layer. This is the top layer of the boards.
Bottom Layer. This is the bottom layer of the boards.