List the breaking changes for version 1.1 here:

• Grails is now Java 1.5+ only!
• Plugins are installed in $USER_HOME/.grails/<grailsVersion>/ by default now, so you will either have to re-install the plugins into your project or change the plugin installation path:
  • Pass the path as the value of the grails.project.plugins.dir system property
  • Add the grails.project.plugins.dir option to your BuildConfig.groovy
• Once a plugin has been installed, the application.properties file is updated. Grails will automatically download and install any plugins missing from the project. Because of this change, we recommend you re-install your plugins even if you set grails.project.plugins.dir to "plugin".
• enums now mapped with string values instead of ordinals (see GRAILS-3076) or by a defined id property (see GRAILS-3633)
• syntax for log4j configuration has changed
• jsessionid is now disabled by default (GRAILS-3364)
• GSP whitespace handling has been improved to retain original whitespace in most situations. GSP output will therefore contain more whitespace (in particular line breaks) than previously. GRAILS-3277
• Some esoteric Gant targets are no longer available ("setupWebContext" for example), but this is unlikely to affect anyone but plugin authors (and very few of those).
• The grails.testing.reports.destDir config option has been replaced by grails.project.test.reports.dir which is more consistent with the other property names. Also, it must be specified in the BuildConfig.groovy file rather than Config.groovy.
• PreInit.groovy is now BuildConfig.groovy!
• "grails.war.java5.dependencies" config option no longer supported.
• Bidirectional one-to-one relationships are now mapped with a single column on the owning side of the relationship instead of two columns on both sides of the relationship
• The grails run-app-https and run-war-https commands have been replaced with an --https argument: grails run-app --https
• These config options have moved from Config.groovy to BuildConfig.groovy:
  • grails.config.base.webXml
  • grails.war.destFile
  • grails.war.dependencies
  • grails.war.copyToWebApp
  • grails.war.resources
• Grails no longer automatically parses incoming XML or JSON requests unless specified in the URL mapping like "/book"(parseRequest:true)
• Bootstrap classes are now run for integration tests (see GRAILS-2089)
• "create-*" commands now create unit tests instead of integration tests.
• The "WarStart" and "WarEnd" events are now fired at the start and end of the "war" target, not when the actual WAR file is created. Use "CreateWarStart" and "CreateWarEnd" for the WAR creation. Also, these events are passed the WAR name and the location of the staging directory.

Some other, non-breaking, changes:

• 'Ant' variable deprecated in scripts: use 'ant' instead
• Pluign authors should use "grailsScript()" macro/method and include "_Grails..." scripts (rather than Init, etc.)