Have you read this:
Bing Keeps Pecking Away At Search Share And Making Gains U.S. Core Search Share, August 2009 (Source: comScore qSearch)
Google 64.6% -0.1% m/m +1.3% y.y
Yahoo 19.3% 0.0% m/m -0.4% y/y
Microsoft 9.3% +0.4% m/m +0.9% y/y
AOL 3.0% -0.01% m/m -1.3% y/y
Ask 3.9% 0.03% m/m -0.4% y/y
Bing (Because Its Not Google) is gaining share.