Google has a checkered history of playing fast-and-loose with search and other data they collect. Tonight, after Midnight, they are invoking a new policy to keep all of your search records.
Of course, other data companies (e.g. Yahoo) are doing similar things, so changing search/info providers may not solve the problem, in the long run.
SayUncle has a link to the Electronic Frontier Foundation to walk you through deleting your Google history before they permanently save it for future reference.
Like sharing with the authorities. As they did in China, and previously, in the U.S.
Sadly, Google is into everything on line. I don’t know if a monthly visit to the above link would help keep your information private, but, it couldn’t hurt!