Tapestry has a big advantage over GWT, the easy separation of the html and all the other stuff. GWT is a little more tricky on that, it's like swing, you are defining your GUI by code (java code) and it's a step back on web GUIs. It's harder for a web designer to touch the GWT code, the tap code is more friendly. It's easier to do a accesible site with tapestry than with GWT.
I saw that the GWT code starts to grow bigger and bigger. See you, Orlando F. Brea