Our friend Peter Thomas has done it again: he has written a great piece about the differences between Wicket and GWT. His conclusion:
Overall, a perception of GWT I couldn?t get rid of while working with it is that it feels like a hack ? but of course, a very well engineered hack. Maybe if you really have a lot of stuff you want to do on only the client side, it is fine. From the perspective of someone used to Java server-side programming, there are too many things about the unique approach that leak through - not being able to do ?view-source? and the added complexity of RPC being some of them.