Globally, Chrome has long surpassed by Safari in usage share, so this shouldn't come has a great shock. StatCounter logged some 3.6 billion page views worldwide, showing Chrome has nearly twice the following with 9.4% versus 4% for Safari. Again, IE and Firefox occupied much of remaining market at 53% and 31%, respectively.
Today's news is both impressive and ironic. Not only has Chrome seized nearly 10% of the US market in under two years, its success is thanks in part to WebKit, the same engine open-sourced by Apple, who uses it in both desktop and mobile versions of Safari.