Here is a list that I compiled from a discussion in g+. Many thanks to Ray Cromwell for sharing the list of projects:
AdWords, AdSense, Flights, Hotel Finder, Offers, Wallet, The New Blogger, Chrome Webstore, Product Search, Public Data, New Google Groups, Orkut, Google Takeout, Google Pagespeed, Google WebFonts, Google Tables, Google Health (discontinued), Google Wave (discontinued), PlayN (basis of Angry Birds)
This is a quite impressive list. Take this into account and the comments from here, than there should be no reason to worry about GWT…
Now that we have a nice compilation of Google projects built using GWT, it would be great to have a compilation of other projects/ companies using GWT.
[update]
So here we go. Please fill out this form sharing information about your “built with Google Web Toolkit” project. We will review and publish the data.[/update]
Thanks to Brandon for sharing the link!


The reference list is now online here:
http://gwtreferencelist.appspot.com/#