I've been asked to code a multi-user web based project in the second week of my internship (in IBM Turkey, by the way), and left the programming language choice to me. First I thought PHP would be easy, but I decided learning GWT and coding the application in Java would be better for me. I started by reading the excellent tutorials in IBM Developerworks ( 1,2,3,4 ).
I had some bookmarks about GWT, and checked them out. One was Googlipse plug-in for Eclipse, which was renamed to Cypal Studio. After many hours of trying to get it to work, I found out that the problem was Turkish locale. Changing the system language to English helped.
Later, I decided to try Instantiation's GWT Designer. It looked great until I added a RichTextArea to my design. It crashed, but when I removed the RichTextArea, everything was back to normal.
I guess I won't be needing any GUI tools for GWT development. Eclipse with Cypal Studio will be enough.