Looking at the IntelliJ blog, it seems that GWT is receiving some attention in IDEA 10.
Thanks for that. While improvements are being made, allow me to point out what's (still) annoying at the moment.
The following issues are in essence blockers for me:
* code indentation in JSNI is still 100% broken. Pressing "Enter" after a line always indents one unit to little (http://youtrack.jetbrains.net/issue/IDEA-55684, and others)
* (gwt) library dependencies are not added to the dev runner classpath - works in IDEA 9, broken in IDEA 10 (http://youtrack.jetbrains.net/issue/IDEA-55571)
The following would be really-nice-to-have improvements:
* when using gwt library dependencies, Ctrl-B navigates to binary class instead of source (http://youtrack.jetbrains.net/issue/IDEA-26915)
* an integrated dev mode runner, instead of the generic Swing GUI (http://youtrack.jetbrains.net/issue/IDEA-56088)
There's a bunch of lower-priority stuff (like proper resolving for JNSI method parameters, for example), but getting the 4 issues above resolved or improved would greatly increase GWT development pleasure for IDEA X.