I've built a prototype for this using various parts. The architecture isn't the best, and I'd like to make it into a proper PCB.
The principal is simple - control relays from an XBee. In actual fact its a high (ish) current 5v output that follows the XBee's 3.3v digital outputs. This is then used to drive a relay, or some LEDs for some nice dim lighting. These output devices can then be controlled using libxbee and some programs - for example, my bedroom light comes on in the morning to wake me up!