Attendance is the first item generally measured to determine the success of a webinar. This is easily done through the webinar reporting system as it will give you 'up to the minute' reporting on who registered and attended the webinar in the live or on-demand format.
Prior to holding the webinar, we recommend making a plan to determine what would make this webinar a success. Knowing this in advance will dictate the feature to be used to allow you to pull reports that will allow you to track these specific items. This effective planning will verify the success of the webinar.