Hello! I'm working on something very similar to you from the ground up. My design is still in progress, but if we could merge our effort, it would be great!
Overall, I plan on using the Pi as the brains of it all and integrate with several things around the house. Using NodeJS gives us the flexibility to run it elsewhere if needed. I'm planning on starting a blog about this as I make progress as well and possibly turning this into an open-source model with some future business potential. I used to develop Access Control Security systems back in 2004-2006 and have learned a great deal about integrated automation.I'm going to target XBee/ZigBee and possibly Arduino/Netduino/Gadgeteer in my automation as well and build a completely automated house including software smarts like automated backup, Natural Language Processing, etc.
I'd be interested in collaborating and I'm open to discussing various designs which could possibly converge our efforts. Let me know what you think.
Thanks,
Nick