A great little paper that examines Facebook users' interactions over time. Perhaps the most intriguing finding is that there is very little consistency of interaction between pairs of Facebook friends from one month to the next - the general pattern is one of occasional spikes and flurries of interaction, with a limited amount of continual dialogue between closer friends. The really interesting thing is that the by far the most common catalyst for the spikes in activity is the sending of birthday greetings. This mirrors real life for me in some ways - I stay in contact with many distant friends largely because of the exchange of christmas or birthday cards but, unlike in real life, a social network makes it much easier to maintain a dialogue.