My project was to implement a "smart power meter", and have it report the collected data to the now defunct Google powermeter API. It achieved this using a dedicated measurement device, a Linksys WRT54GS running linux and a working internet connection.
A minor modification of the Linksys router was necessary for the XBee wireless module to interface with it. This involved soldering header pins to an unpopulated part of the router mainboard, however this was a trivial modification and has not been documented here (a quick google should produce results for many models of router)
The bulk of the hardware was in the measurement device. Schematics and board layout files for this device (as well as source code for the Xmega chip) can be found below in the the Downloads section.
This includes a detailed write up of the project, a complete listing of the source code and schematics of the PCB created.
Schematics and board layout files for the measurement device.
Source code for the Atmel Xmega firmware