Just to beat this dead horse one final time. :
If you haven't considered X10 for controlling your room lights, at least you should know about it. It's UL approved, cheep, and coupled to the Arduino, it gives you lots of options. I made this diagram to illustrate the costs (eBay) and options you have with it.
I would be uncomfortable putting a relay in my house wiring, even if I didn't own my home! 