Valentine's Day!  Well here's a topical research study.  Professor Jamie Pennebaker is probably best known for his research on expressive writing - see, for example, the series of four blog posts I wrote about his lecture at last year's British Association for Behavioural and Cognitive Psychotherapies' conference.  However, as he states on his very informative website, "His most recent research focuses on the nature of language and emotion in the real world. The words people use serve as powerful reflections of their personality and social worlds".  Last month Jamie and colleagues published this interesting paper: 

Ireland, M. E., R. B. Slatcher, et al. (2011). "Language Style Matching Predicts Relationship Initiation and Stability." Psychological Science 22(1): 39-44.  [Abstract - Free Full Text] Previous relationship research has largely ignored the importance of similarity in how people talk with one another. Using natural language samples, we investigated whether similarity in dyads' use of function words, called language style matching (LSM), predicts outcomes for romantic relationships. In Study 1, greater LSM in transcripts of 40 speed dates predicted increased likelihood of mutual romantic interest (odds ratio = 3.05). Overall, 33.3% of pairs with LSM above the median mutually desired future contact, compared with 9.1% of pairs with LSM at or below the median. In Study 2, LSM in 86 couples' instant messages positively predicted relationship stability at a 3-month follow-up (odds ratio = 1.95). Specifically, 76.7% of couples with LSM greater than the median were still dating at the follow-up, compared with 53.5% of couples with LSM at or below the median. LSM appears to reflect implicit interpersonal processes central to romantic relationships.

Interesting!  Do see the six page free full text article and if you really want to explore, try it for yourself at the "In synch: language style matching" page.  As the authors write: "This application determines the degree to which any two samples of language are similar in their language styles. It can be most helpful in analyzing two sides of the same conversation. For best results, use a group of IMs (instant messages), emails, text messages, even transcribed conversations, or even general writing samples between you and another person.  Once you enter your words in the interaction and then the other person's words, you will get a number back that assesses the degree to which the two of you match. This number, called a language style matching, or LSM score, ranges from about .50 to 1.00. The closer you are to 1.00, the more in synch the two of you are.  Other studies have found that the LSM score is associated with how long a relationship lasts and its overall quality".