Michael Jouravlev :

What are benefits of ICEFaces comparing to Google Web Toolkit? This is what I could come up with. Granted, I haven't used ICEFaces yet, so something may be wrong in this list.

Similar features
GWT: J2EE-based, ICEFaces: same.
GWT: Ajax only, ICEFaces: can be rendered with Javascript turned off, but will not submit.
GWT: has basic set of widgets, ICEFaces: same.
GWT: can be easily styled with CSS, ICEFaces: same (?)
GWT: does not need knowledge of Javascript, ICEFaces: same (?)
GWT: UI elements can be properly resized by browser controls, ICEFaces: same
GWT: UI elements can be combined with static HTML, ICEFaces: same

GWT benefits
GWT: views are developed fully with Java, ICEFaces: requires JSF tags
GWT: can be easily debugged, ICEFaces: not so
GWT: clean separation of concerns between UI and server, ICEFaces: ?
GWT: talks to standard servlet, ICEFaces: requires JSF
GWT: widgets are easily extensible, ICEFaces: ?

ICEFaces benefits
???

Old but interesting thread.

ICEFaces vs GWT