I've often filled out comment cards, feedback forms, and even sometimes I've sent compliment and complaint letters. However, I've never really felt that my ideas could change the business to which they were addressed. Usually customers have ideas to improve a business not because they care if the business succeeds, but because they want the experience to be better for themselves.
As much as I'm loathe to say this, Starbuck's is doing something innovative. They are collecting customer (and employee!) ideas of "doable" ideas to improve Starbuck's, and inviting everyone to vote on their favourites. Some are have already been implemented, others are coming. I've often complained that Starbucks doesn't ask if you want your coffee for here or to go, and they don't recycle -- both ideas are high on the list of votes. While this isn't the same as a corporation being responsive and responsible to the community (the shareholders still rule), it is a step in the right direction. And, a good PR stunt, as evidenced by this post. :)
My Starbucks Idea