I've created with a friend a project using Arduino and Android to control the light color of a lamp.
You can see photos, a video and a podcast (video and podcast only in Portuguese, sorry) at his blog:http://www.euandroid.com.br/geral/2011/04/android-arduino-com-alvaro-justen/
The video auto-explain the usage of the system, so you can understand even it is in Portuguese.
The code and schematics are in the project luminaria-rgb on my GitHub account
Future versions will include Bluetooth (this one uses Ethernet with ENC28J60 controller - I'm using my modified Ethernet library
for this work).
Please let me know what do you think about the project.