This presentation from two years ago is still very relevant. The 5 key principles mentioned give me another way of thinking about architecting social media sites (look at slide #40: quick check list). Two years ago the move towards microblogging was just starting; the view shown on slide #72 (blogging vs. microblogging) was at that time a good prediction of the future (i.e. microblogging with Twitter today). - Jeroen De Miranda