I'm quite a fan of Behavioural Economist Dan Ariely's short monthly piece in Wired UK and found his extended feature in the August 2011 issue especially noteworthy. The piece was entitled 'You are being gamed - How online companies trick you into sharing more, joining more and spending more' and analysed briefly some of the ploys employed by organisations such as Amazon, Apple, Groupon, Zynga and Faceobok. Short article; worth the read.
About Facebook, I liked the point about the Wall which I guess applies to Blogging too: We want our Walls to reflect ourselves. Users want to display a self that is somewhere between their real self and how they would like to be perceived.