Google’s Protest Against the Proposed Stop Online Piracy Act / Protect IP Act

Today’s U.S. Google query page has the name blacked out, and a line under the search bar that says, “Tell Congress: Please don’t censor the web!.” I suspect that it makes this among the most widely seen political ads/editorials/statements in American history, at least setting aside statements carried in standard mainstream media programming on historic occasions. Does anyone have a good sense of the number of Americans who use Google on an average day?