A close eye was kept on the volunteers for eight hours after the drugs were given, to check all was well. They were then asked about their experience. Two-thirds of the participants...ranked being given psilocybin as either the best or in the top five best experiences of their lives--on par with the birth of a first child. They described feeling peace, intense happiness and a sense of the unity of all things."
(From The Economist, 15 Jul 06, "The God Pill", pg. 78)

Being no stranger to self-delusion and being a guy who tends to be happy, I found Scott Stossel's book review on Stumbling on Happiness to be pretty interesting.

In an important sense, "Stumbling on Happiness" is a paean to delusion. "How do we manage to think of ourselves as great drivers, talented lovers and brilliant chefs when the facts of our lives include a pathetic parade of dented cars, disappointed partners and deflated soufflés?" Gilbert asks. "The answer is simple: We cook the facts."

The other interesting tidbit is that not everyone is so easily deluded. When people try to strip me of my delusions, I wonder if I should plug my ears, whistle and walk away.

Can awareness of these cognitive mechanisms make us happier, or at least less deluded? Alas, not really. In fact, that's sort of Gilbert's point: imagination (or projecting ourselves into the future) ought to be the key to predicting what will make us happy, but we're incapable of imagining accurately.

Interestingly, the clinically depressed seem less susceptible to these basic cognitive errors. For instance, healthy people can be deluded into greater happiness when granted the mere illusion of control over their environment; the clinically depressed recognize the illusion for what it is. All in all, it's yet more evidence that unhappy people have the more accurate view of reality — and that learning how to kid ourselves may be a key to mental health.

Link

'Stumbling on Happiness,' by Daniel Gilbert - The New York Times Book Review - New York Times