Google has a data center in northern Oregon, in The Dalles on the Columbia River. It's power consumption at full capacity will be (in 2011) an estimated 103 MW. (Google won't reveal its own numbers.)
The total electricity consumption in Oregon in 2005 was 46,457 million kW-hr/yr, or 5300 MW.
So Google will be using about 1-2% of all Oregon electricity (a state of 3.6M people).
The Guardian has another interesting article about Internet power consumption -- it's growing at about 10% a year. US data centers used about 61 B kW-hr in 2006, 1.5% of all US electricity consumption (or enough to power the entire United Kingdom for 2 months), and perhaps will use 80 B kW-hr this year (9100 MW).