I like free stuff. And I like to give my two cents on service experience. (And I have a feeling I'm not the only one.) Put the two together, and you have the overriding reason why so many restaurants and retailers are doing post-purchase surveys on their receipts. The concept is simple - within a short time period after your purchase (usually 2-3 days) you either take a phone or web survey. After taking the survey, you usually get something small for free on your next visit (like an appetizer or a percentage off your next purchase).
Just the other day I was at one of my favorite fast casual restaurants and one of these surveys was included on my receipt. I sat down in a booth with my Diet Coke and figured I may was well take the web survey on my phone right then and there while the experience was fresh on my mind. Here's the catch - the survey had at least 100 questions! (I don't know for sure - after about 50 I abandoned the survey, but based on the progression bar, I was only half way finished.)
While I like the restaurant where I was dining, and want to help improve future service experiences while applauding their great service and food, it wasn't worth my time to finish the survey. (And an unfinished survey is unusable.)
A recent Gartner report ("How to Optimize the Customer Satisfaction Survey Process") recommends that "surveys be short (no more than 12 questions) and focused and tailored for each recipient" in order to maximize response rates. Take the opportunity to look at all of the surveys you're conducting and see if you'd have the patience to finish one. If not, it might be a good time to rework your questions.