a great article from Joscelin Cooper, former UX Writer at Google :
As technology becomes more pervasive and gains access to greater amounts of our personal data, how can we design successful human-machine conversations? Should user interface text approximate the lilt, flow, and syntax of human speech? Or does humanizing UI conversations create a false intimacy that distances even as it attempts to foster familiarity?
The answer, of course, is that it depends. Most of us have encountered voice-automated customer service systems. Some of them, in an effort to make their robot customer reps less droid-like, feature voices that try to approximate human diction. A calm, often female voice pauses, suggests brightly, bridges her prompts with almost-ums. Her attempts at realness further underscore the fact that she is fake, blocking you from an actual human encounter.
A computer that cheerfully calls you by your first name can either delight you or creep you out, depending on the circumstances. Just as robots enter the uncanny valley when they seem too human, a user interface that’s too familiar can push people away. The copy needs to strike the right balance.
Read the remainder of the article on A List Apart