"The biggest challenges efficiency-wise (ignoring luxury items) are transportation, cooking and internet servers. Those are the three things I think are hardest to provide for in a low-energy/resources scenario."

I was under the impression that the energy used for building heating, ventilation, and air conditioning was a significant "low hanging fruit." Relatively small changes in the way buildings are constructed and used could have a huge impact.

For example, in older buildings (e.g. high-end American houses built in the 1930s) there was frequently no arrangement at all for heat in the main entrance hall, staircase, or upstairs hall. But our new McMansions are usually built on open floor plans where the bedrooms and hallways and living rooms and dining rooms all merge together into one big space. Some fairly minor adjustments can be made to this arrangement without too much difficulty--just add some partitions and you can cut your heating bill by 1/3...