Could doing our computing in the cloud which is effectively the data centre save energy? Companies manage their data centre effectively and efficiently, using green energy wherever possible and because they have the incentive to be green on a large scale, it is far more likely to happen in the data centre than at home.
This is where scale really can work. Take apple for example who are currently greening their data centre as we speak. Their efforts mean the consumer needs a less powerful machine and also need not worry so much about their green footprint.