Take a look at below slides. I think this is David Armano's best presentation on Web 2.0 & Social networking -- so far. It concisely and superbly explain what web 2.0 & social networking really is, why it matters, "how it works", and what makes it ticks.
If you have followed the birth and evolution of David's thoughts and ideas the past few years, you will notice that this slide beautifully represent complete composition of "everything David knew" (so far) about the subject. From many perspectives, this final "material" seem almost 100% complete, well tuned, well choreographed ... and splendidly perfected.
Enjoy such inspiring depth and beauty of one of what one day might be known as one of the best visual graphic presentation on the subject of Web 2.0 & Social Networking.