Yes i think gratitude is the single most important thing in all our lives. It is the one thing which if practiced regularly can drastically change our way of thinking and thereby change our lives.
It is not enough to practice gratitude only when something good happens or someone does some good favor for you. Gratitude has to become part of your life. It is simple. You can express gratitude for anything in your life.
I have written a hub on my personal experience with Gratitude. I urge you to read it.