Hi Thomas, we are using GWT from 2006 (a beta version 1.0) and we stopped developing with pure JavaScript (not for Internet sites indeed), and from there we developed about 200 Intranet applications with a very good impact on management.

I think that handcrafted JS is not suitable for Enterprise.

About communication, we first used my own framework for JSON serialization (http://code.google.com/p/productive-gwt/source/browse/#svn%2Ftrunk%2Fgwt-framework%2Fgwt-framework-rest) but now I'm going to upgrade to Errai which is a framework that will us to develop in an homogeneus way client/server.

And also I can stop mantaining that home made framework :)

Which kind of PoC do you plan to write ?