I find it interesting that the fewer questions you have the more time the respondent will spend on thinking through their response and answering honestly. Think about it. You are asking them for time out of their day. So it follows that the shorter and more concise the survey is, the better response you will get from those who take it.
Kipp Bodnar wrote a great article on this subject with graphs and statistics from the research that has been done on survey responses so make sure to take a look.