Came across this on Slashdot that led me to Economist.com...

In terms of momentum—mass times velocity—Google's lead indeed looks daunting. It has by far the most mass, with an American market share of 43% as of April, which reaches 50% counting AOL, an internet property that uses Google's search technology. This compares with 28% for Yahoo!; 13% for MSN, which belongs to Microsoft; and 6% for Ask, which is owned by IAC/Interactive Corp, a conglomerate of about 60 online media brands. Google also has velocity: its market share grew by 17% in the four quarters to this spring, whereas Yahoo! and MSN both lost share. Only Ask has more velocity—its share grew by 35%—but then again it has little mass.

Read the rest at http://www.economist.com/business/displaystory.cfm?story_id=7064434