This was an excellent video for those interested in programming models for distributed systems. Hewitt explains the key features of the Actor Model and makes the case that it more closely matches the physics of distributed systems than other models(e.g. Petry Nets/CCS/Pi Calculus). The Q&A with whiteboard format was very nice -- I got a lot of what I would get by reading an introductory paper on the topic, but in a more entertaining fashion.