A new GWT Designer v5.1.0 Beta is available that supports both GWT 1.4.62 and GWT 1.5RC1 and 1.5RC2.
The initial beta is for Windows only. OSX and Linux support will be rolled out over the next couple of weeks. See below.
This new beta is the result of nearly 600 hours of development that resulted in an almost complete re-write of the GWT Designer core. We are now relying more on the GWT internals and less on our own custom emulations which should improve compatibility with new GWT releases going forward.
This beta should be used for testing purposes only and ideally installed into a clean Eclipse 3.3.2 or 3.4 Windows environment. A production version of GWT Designer v5.1.0 will be released at the same time that Google formally releases GWT 1.5.
The beta can be downloaded here.
Keep in mind that this is a beta and there is a possibility that code that rendered well before will not render well now (or vice versa). We have run the beta over several hundred test cases, but those are by no means exhaustive. If you encounter a problem (exception or parsing / rendering problem), please send a test case (the class and/or project you are editing) plus your complete Eclipse .metadata ".log" file and any ".gwt-log" files found in the .gwt-logs directory of your project to wb-support@instantiations.com (or ZIP up these items and post them as an attachment to a forum message here).
Enjoy!