When I first saw Vaadin I was a bit sceptical: Could the server-side model have even something more to offer? To find this out I decided to re-write one of my peeves, the UI of Hupa in Vaadin and see how it compares to the GWT only version.
Hupa is the webmail of Apache James. It was developed entirely in java, and for the UI we use pure GWT stuff: MVP (Model-View-Presenter pattern), Activities and RF (Request Factory).
So my idea to learn Vaadin, was to re-use the hupa-server backend and create an entire UI implementation using the Vaadin framework.
This was part hobby and part my introduction to Vaadin as a new employee at the company (I now work as a GWT expert at Vaadin).