I don't believe anyone else mentioned it, so here goes...I did a bit of research on these things recently because my wife was bugging me to give her an Xmas list, and I thought home automation might be fun. Several people here have mentioned solutions that require software (often not cheap) that run on a Mac and require that Mac to be running 24/7. The product I added to my Xmas list was
Mi Casa Verde VeraLite which is a network-connected box that handles all of the brain-work. It's optimized for controlling z-wave devices, of which you can get thermostats, door locks, light switches/dimmers, and more. I believe you can also tie into networked cameras. And I believe you can control Insteon and some other devices, too, but I think without 2-way communication compatibility. Whereas, again, it's really optimized to full take advantage of all that Z-Wave devices offer.
I had already bought a Wi-Fi D-Link network cam for about $150 several months back which has a microphone and night-vision. There is already a standalone D-Link app for that, plus I have it set up to send me an email with several still-frames whenever it detects motion. PQ is decent. The back-end software (running on the camera itself - you set it up via a web browser) leaves a lot to be desired, which is where it would be great for a company like Apple to come in and drastically improve that experience. I'm hoping I can view this camera via a central Mi Casa Verde/Z-Wave-compatible iPhone app (it looks like there are several already out there in the App Store).
Getting back to the Mi Casa Verde VeraLite...it sells for about $180. The one knock against it seems to be that setting up "scenes" (e.g., turn on lights A, B, and C when door is unlocked) using it's software (again, I believe this is web browser based) can be tricky. So, again, that's where it would be great if a company like Apple came in. They could take whatever this VeraLite box does and implement it into their AirPort Extreme, so you'd only need the one router box.
In any case...if my wife ends up getting me the VeraLite for Xmas, I'll be playing around with it and see how easy/difficult it is to get working. I'm most interested in controlling a couple of thermostats (about $100-120/each for Z-Wave compatible thermostats) and light switches/dimmers (about $50-85 - ouch). That's my other concern about the whole thing...each little device is kinda pricey, and they can add up to a whole lot of money real quick.