The price of Happiness: $75,000
inc.com
inc.com
"We suspect that this means, in part, that when people have a lot more money, they can buy a lot more pleasures, but there are some indications that when you have a lot of money, you will savor each pleasure less."
So, our perception of happiness is explained by Weber-Fechner Law (http://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law), too, similar to our sensory perceptions: it is logarithmic and saturates after a point.
This is why it is impossible to design a paradise (or hell for that matter) that humans can enjoy indefinitely.
My interpretation of the findings: High incomes typically demand more time away from people and health-inducing activities (e.g., more time spent at the office and on airplanes). There are different stressors associated with low and high incomes. The holy grail is to find that incomes level that minimizes the number and intensity of stressors while maximizing time spent in activities that you control that bring you pleasure.