Just posted my Ajax 101 talk.
I have given this talk in a number of venues starting in January 2006 with Adaptive Path in the Designing & Building Ajax Workshops we hosted in LA, Austin and Amsterdam. I also have given this within Yahoo! for internal training as well as for VeriSign, Federal Reserve, Ultimate Software, United Online and others.
To me understanding web development starts with understanding event handling, model & data services and how to manipulate the DOM. This mental framework is used in this talk (it follows the Model-View-Controller pattern from SmallTalk-80 days).