Just an idea. Many have a spare N900. Some carry their around, for some it could be fun to turn theirs into active being. Scenario:

You come home in the evening, welcomes you bright light already on, turned on by movement of the door (simple to implement I believe), once movement stops in the corridor and has moved to the guest room, lights go out there (tricky part is turning them back on time for wandering toilet seekers) Routines for all kinds of typical activity can be built. Question: does N900 camera suffice for depth analysis? Are two needed to fake a Kinect? Can we plug Kinect to the N900 (or can we find a talented enough person to reverse engineer the driver?) and use its HW?

Two cameras can be used for depth analysis, but it takes a helluva lot of CPU power to do that in X time.

The Kinect, with its IR grid, makes this easier.

Also, you might as well run a full home automation setup with that kind of integration.

Why not? People do this with raspberry pies, though indeed you can get a few of those for a single N900, none of which come with accelerometers, you can 'call' home by steps climbed/GPS data/WIFI data/BT devices around. There was a guy thinking about N900 as helmet protector/proximity alert device. It was a raspberry of its time

Most of the stuff you describe can be done in itself with simple IR-detectors.
However, with the ir-detectors connected to a computer of some kind gives a lot more flexibility.

Personally i use plain IR detectors for the lights in the hallway and the bedroom. For livingareas and the kitchen i use a timer that turns my LED-lights on and off after the suns movement, and also is connected to the network.
-That is done with a Dovado router and a Tellstick.
http://www.dovado.com/index.php?opti...d=68&Itemid=17

Then i have written a small program in python with telnetlib on the N900 to log into the dovado router and turn on or off the lights at will.