This is another frightening thought regarding your e-mail “privacy“. Although this ruling was for different circumstances than Google's AdWords in your GMail inbox, it does support Google's ability to do so.
source: http://www.newsfactor.com/story.xhtml?story_id=25730
Three judges debated the Wiretap act of 1968, the Electronic Communications Privacy Act of 1986, the Stored Communications Act, and various cases of electronic snooping before ruling that it was okay for an Internet service provider to eavesdrop systematically on the content of e-mails and use the information it gleaned for commercial gain.