Hi, I'm working on a HA project right now as my first Arduino project. It's going to be a centralized system with ONE Arduino Mega based custom made controller with a lot of digital inputs, solid state outputs on 220V and 12/24V, and dimmer type outputs from 0V to 220V. Analog inputs also 
This type of HA type requires a special wiring, not the regular one. Every cable must start from the controller to the controlled object (lamps, motors, etc.).
The objects will be controlled either by wall switches (normal push buttons), or by touchscreen tablets/smartphones/laptops... just everything that has a browser and WiFi. This is how I do it:
Device with WiFi -> WiFi router -> PC -> Arduino
Right now I'm doing a research on the best interface technology. I like Flash/Flex, but Apple (iPhone) doesn't 
The new Windows Phone 7 OS that was introduced by Steve Ballmer today, well... also doesn't support Flash. Android is on the right way, however. There is however an option to go with a "native" apps for the unsopported platforms. A regular HTML/JavaScript interface is much more easy to do, but where is the fun?! 
P.S. EriSan500, I like your notes. What's the status of the project?