Its benefits as stated in http://code.google.com/webtoolkit/overview.html
- Dynamic, reusable UI components
Create a Widget by compositing other Widgets. Lay out Widgets automatically in Panels. Send your Widget to other developers in a JAR file.
- Really simple RPC
To communicate from your web application to your web server, you just need to define serializable Java classes for your request and response. In production, GWT automatically serializes the request and deserializes the response from the server. GWT’s RPC mechanism can even handle polymorphic class hierarchies, and you can throw exceptions across the wire.
- Browser history management
No, AJAX applications don’t need to break the browser’s back button. GWT lets you make your site more usable by easily adding state to the browser’s back button history.
- Real debugging
- Browser compatible
Your GWT applications automatically support IE, Firefox, Mozilla, Safari, and Opera with no browser detection or special-casing within your code in most cases.
- JUnit integration
GWT’s direct integration with JUnit lets you unit test both in a debugger and in a browser…and you can even unit test asynchronous RPCs.
Easily create efficient internationalized applications and libraries.
- Interoperability and fine-grained control
- Google API Library: Google Gears support
We are in the process of building support for using Google APIs in GWT applications. Initially, we are providing support for Google Gears, the recently-launched developer product that extends the browser to allow developers to make web-based applications function even while offline. If you would like to download this library please visit the open source project. We are planning to add support for other Google APIs; if you’d like to help, please check out Making GWT Better.
- Completely Open Source
All of the code for GWT is available under the Apache 2.0 license. If you are interested in contributing, please visit Making GWT Better.
- Google Developer Day US – Fast, Easy, Beautiful: GWT. [youtube=http://www.youtube.com/watch?v=NvRa-CxkpZI]
- Voices That Matter: GWT – Architecture Best Practices. [youtube=http://www.youtube.com/watch?v=Uwp3EVU5ePA]
- Voices That Matter: GWT – Productivity [youtube=http://www.youtube.com/watch?v=C5qYJsIWufA&feature=PlayList&p=24044DF77EB53015&index=7]
- Voices That Matter: GWT – Usability [youtube=http://www.youtube.com/watch?v=kMsL9fN-rXk&feature=PlayList&p=24044DF77EB53015&index=4]
GWT uses widgets, the equivalent of components for VB, swing etc. The original GWT incorporates few widgets. On the top of my head come some other extensions
Food for thought:
Also there is Google Gears…