The Ajaxian has just posted their review of the book .

This is not the reference “bible” for GWT, though it does contain more reference material in one place than any other source so far, so you’ll have to wait for that sort of reference work. But for anyone wanting to get a jump start on GWT, start developing applications, and understand what all the fuss is about, I heartily recommend this book.

Robert Hanson has put together a Google Maps-like widget called ViewportViewer.  It enables you to show a viewport of an image that is larger than the viewport itself.  The APIs are not final yet, but he’s looking for comments before its inclusion into the GWT-Widget Library. Looks really cool!
Demo

Chronoscope, developed by Ray Cromwell, is a GWT based platform for creating interactive charts.

Chronoscope is a visualization platform under development at Timepedia for time series datasets. Chronoscope stems from a desire for responsiveness and interactivity when navigating or authoring datasets. Ultimately we aim to bring something like the experience of Google Maps or Google Earth to time series data.