I feel it is very important to show gratitude to those who do for us. I try to show others gratitude on a regular basis (but not so much that it becomes disingenuous). As a teacher I try to teach children that they should show gratitude to their teachers, parents and friends for the things they do to help them out.
Showing a lack of gratitude looks like people are taking things for granted. It won't take long before others lose their motivation. Generally, people don't do things for the accolades, but a simple 'thank you' is all most need to keep going.