There are three total PC boards for this project: the Arduino Deumilanove (now called the UNO), the ethernet shield and a protoshield that plugs into the top and holds the circuits required for measurement of the AC voltage and current waveforms. This part of the project won't need an LCD display or control panel - it will be mounted next to the main power feed for the house, in a weathertight plastic box.
Some customers have complained that the ethernet shield sits down too low on the Arduino. They must have fixed that problem, mine sits high enough to clear the USB connector on the Arduino. I'm hoping the shield will work without the need for any hardware modifications. So far, things look pretty good.
I've been considering using an Arduino "Pro" from Sparkfun: http://www.sparkfun.com/products/9219 because it seems much more durable to solder the arduino and the ethernet shield together. You're certainly guaranteed the ethernet shield won't possibly touch the Arduino that way, and I like the idea of committing a lower-cost, solidly-wired Pro for the project. I'll consider swapping out the Deumilanove for the Pro after I get all the kinks worked out.
I started assembly of the protoshield tonight. First the basic components that came with the shield. Here they are simply placed on the shield, not soldered down. It won't look that bad when it's done....
The red shield will then get the components for the voltage measurement circuit. Test only those components, then assemble the current measurement circuit and test those. The prototyping area on the shield is very, very small, so I want each section to work before moving on to the next one, or it'll be a mess.
I'm thinking about adding temperature sensing to this project. It would be helpful to see how outside air temperature changes compare to energy usage.