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

Luis

Answer: 
Right now you cant use Groovy on the client side. One big reason is that Groovy relies a lot on introspection, and this is not available on GWT.
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).