Now and then I give feedback to a store. More shops now seem to request opinions from customers. Usually I fill out a form online and I am more likely to do so if a 'reward' is offered. Sometimes I don't get around to using the voucher before it runs out. Often there are conditions such as spending a certain amount of money and I may not think it is worth while.
Yes - but I don't do it for the reward. Generally in life, the complainers are more vocal than those who have enjoyed good service. This being the case, I quite often advise a company if an employee has gone above and beyond the usual duties attached to the position. It's only fair, after all.