Developing webapps in Seaside is a lot of fun. The ability that Smalltalk gives to you in terms of having a live coding environment, coupled with being able to debug and modify Seaside code in the browser while in development mode, is really powerful. When I first started learning how to program, learning Pharo and Seaside was of tremendous help in understanding how things work. After having used components to build webapps in Seaside, I was simultaneously amused and saddened when I saw it hailed as the next big thing years after Seaside had already done it (disclaimer: I've probably now opened myself up to someone telling me that it was done before Seaside did it!)

The free "Dynamic Web Development with Seaside" book guides you through creating an ajax webapp, but the last time I checked the chapters on persistence were kind of weak. That being said, for toy webapps it's sufficient to just save the state of the Seaside image, with a singleton as your "database".