This is awesome: http://www.newscientist.com/article/dn19200-twitter-mood-maps-reveal-emotional-states-of-america.html
In short, some researchers in Boston searched 3 years worth of tweets and scored each tweet using the Affective Norms for English Words word-rating system. E.g, words like,
“diamond”, “love” and “paradise” indicate happiness, whereas “funeral”, “rape” and “suicide” are negative. “Dentist” is fairly neutral.
Using geographic information from each Twitter user’s account, they then made color-coded maps of moods in the US over time. This is interesting:
[The validity of the results] is particularly marked when the daily mood maps for the west and east coasts are compared: the west coast mood follows the same pattern as the east, with the 3-hour time-zone delay, indicating that each coast experiences the same time-dependent swings.