When you have a bad experience with a company's service or product, writing a complaint letter can be a highly productive way to vent your frustration and often get something for free that you'll actually use. Here are some examples of things I've received in response to complaint letters I've written.
Gap - $15 gift card
Luna Bar - Six Luna bars (total value: $7)
Amy's Organics - Coupons for free items of my choice along with a few $1 off coupons (total value: $16)
Apple - my computer fixed for free and a Pro Care membership (total value: $375)
Calling can also be effective, if that's what you prefer, but I find letter writing to be both fast and effective--there's no bouncing around automated systems, holding, or pleading to speak with a manager.
As someone who regularly writes complaint letters, I also make it a practice to write compliment letters whenever I have a particularly good experience with an employee or a company. It just seems like a good idea to maintain that sense of balance and to try to appreciate things at least as often as I moan about them.
Photo by heatherrrrrrr