The amplesdk is very interesting idea that you can use all javascript and markup languages to provide a RIA feel to a web application. This could be used nicely with the new spring 3.0 REST annotations if you want to just serve pages that react to xul, json, etc... via javascript interpretation.

The ample sdk could be used as a replacement / augmentation of a flex front-end. The approach for each is pretty much the same in relation to the backend application architecture.