This is something you don't see every day: Google's market share in search for US has dropped from 44.7% in June to 43.7% in July, according to data from comScore Media Metrix. After 11 months of consecutive gains, Google search drops one percent, and that results in more market share for Yahoo (up from 25.5% to 25.8%), AOL and Ask.com.
Here's a chart that shows Google's US market share in the first half of this year, as measured by the same source.
We'll see next month if this is a trend, and Google's traffic acquisition deals aren't effective, but, most likely, this is just a transitory decrement in popularity.
Update: Nielsen / Netratings says that Google's US market share in July was 49.2%, down from 49.4% in June.