Google now more than a search engine
The problem with privacy and security is it is limited by the skill of people.
Google is now an email, and apps company. If I choose to use it for things other than searching for information then I am relying both on the integrity of all Google's employees and the benevolence of the government of any country that Google has servers in. Do I trust either, with my day to day personal communication probably yes, there is not much they are likely to be interested in. When it comes to confidential client information or business plans I would expect to trust them to the same degree as I trust postmen around the world not to read my postcards.