There was a recent article on an experiment in The New Scientist which explored human/robot interaction.
They took three rooms of people and put a friendly robot in one room that hung out with them and was very funny and friendly and really helpful to the people in the room. They took another room and they put in a stern robot, a not so friendly robot, a serious robot. Then in the third room, they put no robot at all. They acted friendly or stern prior to the test, once the test started they just sat in the corner and didn’t say anything.