100 billion searches a month are made on Google

"A stat we haven’t heard from Google for a long time. How many searches it handles: 100 billion per month."

Source:  SearchEngineLand, 8th August 2012

Earlier - 1.2 billion a day in 2007 - warning - different methodology

Note:  The 2012 figure could include all of the searches on Google properties, especially those on YouTube.  Bt if not it shows a 2.5 x increase in 5 years - 1.2bn in 2007 vs 3.3bn in 2012