NB! Grails plugin is disabled by default.
The plugin is being under development at the moment, so no special treatment of Grails application is done by JRebel yet.
Grails handles live updates for controller/service classes very well by itself. What Grails doesn't do, is reloading the classes that aren't a part of grails app.
The good news is that the non-Grails application classes are handled by JRebel once you have it enabled.
Also, when changing Grails application classes, Grails will to redeploy the application in development mode, which may take time for the application to initialize, and you may also loose some data with that. To disable automatic re-loading of the Grails application you can either add -Ddisable.auto.recompile=true to the startup parameters list, or enable the Grails-JRebel plugin that does the same for you.
NB! Currently there's no support for domain classes reloading. Thus, once you make a change to any of your OR-mappings, you still have to restart Grails application.