In a 12 foot by 12 foot by 12 foot foot print, I have a full size bedroom, bathroom, kitchen and living area. On demand hot water, furnace, backup power. The Cube is a completely green structure and is a comfortable place for one or two people to live full time, and with enough space to sleep 4 occasionally!
It took almost a year to get it perfect!
http://www.youtube.com/user/TwelveCubedHomes?feature=mhee