One of the little time-saving tricks I use in my home automation system is setting the Ethernet MAC address automatically on each device. This saves having to set the address manually in the sketch of every device.
I've written it up in a tutorial on the Freetronics site:
If you're just getting into home automation and go searching for Open Source HA projects, you'll discover there aren't any obviously dominant players - more a mix of partly-developed personal projects that aren't very portable. Why is that?
As part of my @SuperHouseTV home reno the entire house has been rewired, including replacing all the light switches with Freetronics Arduino-compatible control surfaces running on the LAN using Power-over-Ethernet. To save time assembling all the switches I designed a custom PCB for the control surface.
Early in 2011 my family was flooded out of the SuperHouse when water came through the ceiling during renovations, and for many months after that we lived in the recently built workshop at the back of the garage. Well, the garage flooded as well. Oh joy. And to make it even more interesting, I learned a lesson never to leave running electrical equipment on the floor. Or to stand next to it, in water, while it's running.