In case you weren't already convinced, I thought I'd share another example of how expressing your opinion to a company about its products is quite often effective.
I recently ate a bag of Terra Chips that I was not quite enthused with. The overall flavor was good, but they were much too salty. As I was about to throw the bag away, I noticed a statement on the back that I should write to them and send the empty bag if I wasn't completely satisfied. So I did.
In a few weeks, I received a letter, two coupons for a free, full-sized bag of Terra Chips, and two coupons for 55 cents off. Since I have been eating a lot of Terra Chips lately and they aren't cheap, I'm quite happy about the coupons.
To read about my previous success with writing to companies, read about My Consumer Victory With The Gap and How I Get Coupons for Organic Products.