I remember when you asked that question at google i/o.
We're using gwt for a reference implementation of itemscript, an open source json schema project. It does take some time to get it set up right, but when you do...
GWT is reveling against it's next constraint right now, the support of a growing developer base, not all within Google.
I used it on a large project, and enjoyed using it despite some rough edges. Most of these rough-edges turned out to be not based upon what GWT is, but how I was using it.
First, GWT is free-form and it's up to you to have a good internal architecture for your large, complex application. Fortunately, Ray Ryan gave an excellent talk at Google I/O this year which addressed all of the architectural questions that came up during my first project. My team is now embarking on an even larger project, and we have implemented the pattern described in Ryan's talk - and it is fantastic in terms of flexibility. We're very confident that we'll be able to tackle whatever ambitious requirements come up.
I've made myself watch this talk about 12 times, and each time I keep pulling out some essential bit of wisdom. Now, there's a lot of stuff in there that might be obvious to someone who uses other languages/frameworks for making GUI applications. The HandlerManager eventBus that he's using is really the same thing as NSNotificationCenter, for example.
But for someone coming from a web or JEE background, this presentation was pure gold.
The second way in which I was using GWT wrong in my first project was I was compiling my app each time rather than staying in hosted mode. The reason for this, however, was because we didn't understand the value of hosted mode early enough in the project...and so programmers committed changes that made hosted mode stop working (through missing configuration that made hosted mode need to connect to an app server in order to debug). Had I known a bit of Ray Ryan's wisdom, I would have written a single RPC call following the command pattern and mocked up a dummy service for use in GUI development.
Another minor thing was that we were using Netbeans rather than Eclipse. While I love Netbeans, and hate Eclipse, the GWT team has made Eclipse a well-worn path and it's really slick. The GWT4NB plugin gives one the impression that they need to go through an agonizingly long build process every time they make a change. Turns out, this was not true.
We're using gwt for a reference implementation of itemscript, an open source json schema project. It does take some time to get it set up right, but when you do...
GWT is reveling against it's next constraint right now, the support of a growing developer base, not all within Google.