Some of the scenarios Lee walks you through:
* Sexy client-side Calendars (that can be built / communicate with the server)
* Auto-completion (a la GMail’s compose recipient, etc)
* Form validation (that leverages Ajax)
* Dynamic thumbnail generation
The book then walks one through creating a real-world Ajax-powered photo gallery app. Lee also touches on interacting with SOAP web services and the Google Maps API.
All in all, definitely worth a read if you are a PHP developer and are looking for a good primer on Ajax-based technologies.