Question: Is it possible to develop an application in groovy using GWT components?

Luis

Answer: 
I don't think so, because the GWT compiler is basically a [Java to JavaScript *source*](http://java.dzone.com/news/understanding-gwt-compiler) compiler (it would be possible if the GWT compiler needed Java bytecode). You can use Groovy on the server side though.
I have also wondered this, as it would be very nice. Vaadin essentially does this and you can use their plugin: <http://grails.org/plugin/vaadin> 

Doing it this model, though, it is compiling components into Javascript and delivering from the server. But unlike GWT components, these are calling back to the server every time you touch the API (though of course with Vaadin you can use GWT components as well).