I am interested in the possibility that GWT could serve as the basis for my entire presentation layer.
I would be interested to know if anyone has tried this successful
You mentioned that GWT would handle the presentational layer. Would you be doing the business layer in Java too? If that's the case, I'd like to point you towards IT Mill Toolkit, that does exactly this: It's a toolkit that uses GWT to render its GUI components, allowing you to do your applications entirely in Java. I think the term it's trying to coin is "server driven RIA".
I come from a PHP background, but instantly came to like the toolkit. But it's probably better that I won't say anything more and let you do your own decisions.
Disclamer: I do work at IT Mill, although that's irrelevant to my opinions.