In 2010, in the USA, datacentre electricity use was 2% of the national total electricity use. Worldwide, datacentres use about 30 billion watts of electricity, roughly equivalent to the output of 30 nuclear power plants. This is probably on a rapid exponential growth rate (anyone know?) so while it's astonishing to see so much energy being used to power the computronium, it's also a huge opportunity for energy savings.