You don’t get much better than Danny Sullivan’s article on July’s comScore figures. The article provides a fantastic overview of search engine statistics on the whole, comScore’s figures in specific, and makes a valuable point about the care it’s necessary to take when looking at any interpreted statistical data.
Read the report yourself, then decide whether Google has actually lost "market share" – and, more importantly, whether it even matters!
Do not put faith in what statistics say until you have carefully considered what they do not say.
William W. Watt quoted in "Medical Statistics: A Guide to Data Analysis and Critical Appraisal" by Jennifer Peat and Belinda Barton