It is important to strike a balance between having enough respondents to give representative feedback and making too much work for not enough benefit. Bear in mind that if you are running a 360 Degree Feedback project and you have too many respondents for each subject then a large number of questionnaires will be generated and people will get fed up of filling them. Also some subjects may feel that there aren't enough people who know them well enough to give quality feedback. All things considered six respondents is usually about right. It can work well if the trainer asks the subject for a larger number of potential respondents and then chooses six at random.