Average Power Use Per Server & Desktop
The ars technica folks published this informative breakdown of server power consumption in 2007, credited to "Intel and EXP Critical Facilities":
Note that this does not appear to include cooling and other related power energy use. Jonathan Koomey's landmark 2007 analysis that suggest an average US server consumes only 472W, including cooling, etc. at 1X power consumption (PUE 2.0). A 2009 IBM analysis uses 425W at "average load", but this does not appear to include cooling.
The equation is being shifted by new technologies, ranging from small-scale servers that typically run under 100W to new volume servers that offer 500+ CPUs consuming less than 2kW in total. As computing shifts to the more efficient cloud, PUEs are also improving. Koomey uses in his 2010 work PUEs in the 1.92-1.83 range.