We have a large GWT code base, although others here work on it more than I do.<p>Problems that seem to get mentioned a lot:<p>1. Difficult to develop or debug without custom IDE plug ins.  With Google cutting back on their investment, not clear how well those plug ins will be maintained in the future.<p>2. Awkward to work with Javascript libraries, at least compared to all Javascript development.<p>3. Sometimes hard to predict exactly what Javascript will be emitted for specific Java code.<p>4. Remembering the rules for what Java code can or cannot be compiled by the GWT compiler.<p>5. A lot of indirection.  The event model has definite benefits, but it also seems to make it very hard to figure out what the program will do by just navigating the code.<p>6. Difficult to find developers willing and able to work on a GWT code base.