Figuring out who people are by studying their word choices

He Counts Your Words (Even Those Pronouns) . James W. Pennebaker's interest in word counting began more than 20 years ago, when he did several studies suggesting that people who talked about traumatic experiences tended to be physically healthier than those who kept such experiences secret. He wondered how much could be learned by looking at every single word people used — even the tiny ones, the I's and you's, a's and the's.

From the linguist discussed in the article: Wordwatchers, a blog which tracks the candidates' words in the 2008 presidential election.