A new paper comparing income to happiness, mostly as national GDP.
Wealthier countries having happier people makes sense: a wealthy country can afford to have a well fed, clothed, housed, and entertained populous.
But at the same time the US serves as a counter example, and this also makes sense. While GDP gains in many other advanced nations (e.g. most of Europe) have also lead to increases in social insurance (i.e. "welfare") programs, in the US the opposite has occurred. We have had a big jump in GDP, but most programs for the poor have gotten less generous, and social security, medicare, and medicaid are constantly in danger of cuts by politicians [on the right...including Obama].
Our social safety net is getting weaker as our country has gotten wealthier. That is a recipe for unhappy people, even when people in general have more money. Someone making $30k/year who doesn't have to worry about losing health care, her house, and having problems getting food for her child is going to be more content than someone making twice as much that has to concern herself with those things. Even someone making $100k a year in the US can quickly find herself in dire straits if she looses his job. Mortgage/rent can eat through savings fast, and a single visit to the ER can be thousands of dollars (and COBRA is not cheap).