I've lost count of how many times I've filled in alaskalistens.com surveys. Usually it's to praise the flight crew (e.g. I had a FA working F on her second full day being a flight attendant. She did a great job so I sent in kudos via the site). Sometimes it's because the cheese plate is nasty. Once it was because they forgot to cater the plane in Seattle for the return flight so there was no hot meal in F. That one got me a $50 discount code for future flights. All others? No response.
Neil