I did a little research a while back. Here are my notes;
m-gwt
http://code.google.com/p/mgwt/
Set of mobile widgets and transitions for GWT. The widgets are quite
good and work on desktop, tablet and phones. My Android 3.1 tablet
has trouble with the history, but that is a small problem. The
library is well integrated with standard GWT. It uses CSS3
transitions and animations for efficiency. It uses separate CSS files
for each browser profile, so it is easy to use the correct sizes and
transitions based on browser type. Integrates with gwt-phonegap to
create installable applications. The associated blog is also very
informative.
There is a demo site to show how mGWT performs in mobile and desktop
browsers. It is a single site that uses different CSS to display
itself for these different form factors. mGWT performs more smoothly
than GWT Mobile, but it does not have as many widgets and features.
It works well on an Android phone, Android tablet (that is
impressive) and desktop webkit browsers. It does not work at all on
IE9 (so, more work would need to be done to create a browser profile
for IE). The history management works well in both the desktop and
mobile browsers, which is a big advantage over GWT Mobile.
GWT Designer was recently updated to support mGWT, so it is well
integrated with Google’s tooling.
GWTMobile
http://code.google.com/p/gwtmobile/
GWTMobile is a framework that includes mobile UI widgets, a
persistence api and a phone-gap wrapper. The Android store has two
demo apps that can be installed.
The apps run using GWT-PhoneGap and perform pretty well on an Android
phone. I would say most of the transitions are not that good. The
mGWT transitions work much better.
There is a separate browser demo for desktop and mobile. In both
cases, the views are formatted for a phone (the desktop site runs in a
picture of a phone). The mobile demo works well on an Android phone
and feels almost identical to the demo app, except the history
management is broken. I keep hitting the back button and leaves the
demo site, which is very aggravating. Again, the transitions are
better on mGWT, but GWT Mobile has more user interface widgets.
The demo site does not run on IE.
CAVEAT: I have not used either of these libraries. I looked at their
demos on desktop and mobile browsers. I also downloaded the mobile
apps (both based on PhoneGap).
Ed