Google collect information, and use it to profit. From Google ​privacy policy:

Google collects personal information when you register for a Google service or otherwise voluntarily provide such information. We may combine personal information collected from you with information from other Google services or third parties to provide a better user experience, including customizing content for you.
...
We may use personal information to provide the services you've requested, including services that display customized content and advertising

Sites that use Google Analytics service provide Google with information about their site traffic, and more importantly, about their visitors movement across the Internet. and the users never have to agree to Google privacy policy!
the larger the number of sites using Google Analytics, the more complete Google's picture will be.
Another issue is, that even if Google is an angel, if and when the American government will force it to disclose its information, by setting a new law for example, it will do it.

This leads me to believe sites should not use Google Analytics services, but use their own local services. FireStats is one such service, but there are many other.