I just wanted to offer a rebuttal to the following tweet that popped up on my stream today:

@GuyKawasaki The reward system actually reduces motivation http://om.ly/MHzl

First, let's take a look at the cited study.  The experimental groups were defined as:

The children were then randomly assigned to one of the following conditions:

1. Expected reward. In this condition children were told they would get a certificate with a gold seal and ribbon if they took part.
2. Surprise reward. In this condition children would receive the same reward as above but, crucially, weren't told about it until after the drawing activity was finished.
3. No reward. Children in this condition expected no reward, and didn't receive one.

While reading this study, we have to ask ourselves: Is a "certificate with a gold seal" really a reward?  Is that what best motivates children?  Do the results of this study conclude that children don't change their behaviors for rewards, or simply that the reward itself was lame?

Despite what the authors state, small rewards CAN be a powerful impetus for behavior change.  Reward is a staple of behavioral training, and in particular, rewards that release dopamine (e.g. food, sweet beverages, etc.) strongly influence brain plasticity during a training event.  To make a blanket statement on the contrary is dangerous.  Preventable disease is a huge drain on our health care system, and it's been shown that simple behavior changes like diet and exercise can reduce the burden caused by obesity, diabetes, and heart disease.  Just because a child responds in a certain way to a reward of a certificate with a gold star, I don't think we should abandon the proverbial "carrot" when trying to get people healthy.