Here's this 27 page research study (pdf file). The study estimated Google used 16.5% of all U.S. consumer Internet traffic in 2008, and that share is estimated to grow to 25% in 2009 and 37% in 2010. What drives this conspicuous bandwidth consumption is Google’s search bots regularly copy every page on the Internet, some as frequently as every few seconds, and Google’s YouTube streams almost half of all video streamed on the Internet. Source: Google uses 21 times more bandwidth than it pays for -- per first-ever research study