Mental Floss this month cites a study* that found that if you add one "happy friend" to your life, that your probability of being happy yourself goes up by 9%, and that's worth about $45,000.
I still generally assert that happiness comes from keeping the commandments, but still, if those findings have any truth to them, I need to reassess my net worth.
I wonder if we should be actively trying to befriend happy people. If one happy person can make several new friends happy simultaneously, and they in turn, the world would obviously be a happier place.
* How Do I Put a Price on Friendship, Jul-Aug 2010, p21, citing a study in the British Medical Journal.