I love it when this happens. A team of psychologists at U.C. Riverside took a look at happiness and the things that go along with it. As the Guardian puts it:

The findings suggest that happiness is not a "feelgood" luxury, but is essential to people's wellbeing. What is more, happiness can also extend across an entire nation, with people in "happy" nations being more likely to have pro-democratic attitudes and a keenness to help others.

You don't say. But wait, there's more:

"Almost always it has been assumed that things that correlate with happiness are the causes of happiness, but it could be just the opposite — that those things tend to be caused by happiness," said Professor Ed Diener from the University of Illinois, another author on the paper.

Now this is interesting. I read a Zen book a while back that stressed the point that, in any causal situation, the effect is also a cause, and the cause is also an effect. (There's a whole big Zen-ish rant on the inherent bogosity of all dualistic models I could spin out right here, but I shan't.) So, what does happiness bring ya?

"There was strong evidence that happiness leads people to be more sociable and more generous, more productive at work, to make more money, and to have stronger immune systems," said Prof Lyubomirsky.

So let's see. Be happy, stride right on out into the universe and create your own reality, and you have a good chance of finding yourself in good health, living well? Actually, that sounds about right. Good work, science!