There was a lot of buzz last year with Are your friends making you fat?

There is extensive documentation on what many call the Framingham, Mass. longitudinal study, where they studied as many people in the small town for as many years as they could. I think the results of that are the most reliable on the question of the "contagiousness" of happiness and sadness.

See my reply to DanielVarga above.

I also mentioned other interesting tidbits from the same book previously. Guess I should do a summary here soon.