The very cool Ajax4jsf project now has some excellent integration with the Google Web Toolkit, and Sergery Smirnov has written a tutorial showing how to use the two libraries together. He also states:

The mission of the G4jsf subproject is to shift the perception of the relationship between GWT and JSF from viewing them as competitive technologies to viewing them as naturally complementary technologies.”

Interesting stuff - the Ajax4JSF library has been very useful to us, and I expect the GWT integration will be of equal quality. This opens some exciting new possibilities for using JSF and GWT.