Eric Schmidt was quoted by Financial Times to say: "The goal is to enable Google users to be able to ask the question such as 'What shall I do tomorrow?' and 'What job shall I take?' ". While the questions seem tough or too important to be answered by a search engine, Google's goal is to transform all the information gathered from your queries, actions and options into something useful. Unlike your ISP, Google allows you to use its search engine without creating an account and is transparent about your options.
Of course, a personal assistant needs to be trustworthy because you provide it with your personal information. It also needs to show up at work whenever you need it, anticipate your actions without being annoying, do background researches to answer your questions properly, prioritize information according to your interests.
Who knows, maybe in the future Google - the personal assistant - will know more about you than yourself. But it will hopefully be more subtle than the now defunct Clippy.
Creative Commons-licensed by bsimser.