How do I know how many customers are seeing but not responding to my surveys?
There are a couple of ways to view this information.
Summary: For a summary, open your survey Project and look at the Dashboard. In the top-right, you'll see a box titled 'Surveys'. You can select a date range and it displays the number of responses (middle column) with number of surveys displayed (the 'n' value) for each channel of web, email, and event.
Detail: To view the detail of number of times a survey is displayed or sent to a recipient versus the number of responses, look at the Trends tab on your Dashboard. You'll see a graph titled 'Daily Number of Respondants by Channel' - select the date range and you'll see the number of surveys vs the number of respondants by day.
The first summary is great to get a snapshot of how effective your campaign is. The second helps you work out on which day your recipients are most responsive (eg Tuesdays).