OS X
Configuration
~/Library/Preferences/<PRODUCT><VERSION>
Caches
~/Library/Caches/<PRODUCT><VERSION>
Plugins
~/Library/Application Support/<PRODUCT><VERSION>
Logs
~/Library/Logs/<PRODUCT><VERSION>
where <PRODUCT>
is IdeaUE (IntelliJ IDEA Ultimate Edition), IdeaIC (IntelliJ IDEA Community Edition).
To use Dropbox, simply sync Configuration directory