If you install build 9618, be aware that the idea.properties file (<idea-installation-dir>/bin/idea.properties) intermixes the setting of configuration directories. Some of the properties point to .IntelliJIdea80 while others point to .IntelliJIdea8x (introduced in the 8.1 EAP builds).(See below.) You may want to edit this file before launching this build for the first time so all the properties point to .IntelliJIdea8x (of what ever you had previous 8.1 EAP builds set to). I was missing recent configuration changes, projects in my project history, and plug-in upgrades when I first started using this build. http://www.jetbrains.net/jira/browse/IDEA-21375 has been opened on the issue.

# path to IDEA config folder. Make sure you're using forward slashes
idea.config.path=${user.home}/.IntelliJIdea80/config

# path to IDEA system folder. Make sure you're using forward slashes
idea.system.path=${user.home}/.IntelliJIdea8x/system

# path to user installed plugins folder. Make sure you're using forward slashes
idea.plugins.path=${user.home}/.IntelliJIdea80/config/plugins