I recently connected with a number of college friends via a social network - LinkedIn (BTW, my LinkedIn profile can be accessed here). I found the responses very interesting and somewhat humorous. No guarantee that you will agree.
I knew each of the individuals reasonably well, although I wasn't extremely close to any of them. I sent a similar greeting to each of them, but the responses were very telling, and matched very closely to my expectations. The audience was two women and one guy. The guy's response was what I would expect from a guy - three sentences - one saying thanks for contacting him, one saying he was doing fine, and one question back to me. What else would you expect? The two women's responses were very much in line with their personalities as I knew them nearly 20 years ago. One was deep, contemplative, and much more personal in nature which matches her quiet and calm demeanor. The other was frantic and hectic - some words in ALL CAPS, many and multiple exclamation marks!!!, and multiple question marks???. This also matches her personality. I had to laugh at the contrast between the three responses. It was also telling that while I haven't interacted with some of these individuals in 15 years, the structure of the responses was right in line with what I expected.
I am sure that email communication and social network communication/connections are providing deep research opportunities for psychologists, sociologists and social anthropologists. I think the real challenge for the researchers to get a complete picture is to bridge all of the various social networks, blogs, email, IM, and then direct communication (does anyone really do this anymore?). More and more aggregation services are becoming available, but each one in turn introduces more options to the equation.