There is a new science of happiness. An article Against Happiness in the current NY Times Magazine by Jim Holt reports on experiments that show that happy people tend to be more judgmental, i.e., more like angry people, than like sad people, who tend to be nicer.
One of the leaders in this field is Daniel Kahneman, who recently gave the Marschak Memorial Lecture at UCLA.
Here is a transcript of a radio interview he gave in August 2003. All In The Mind - 17/08/2003: Nobel Laureate Daniel Kahneman: Toward a Science of Wellbeing. It's worth reading.