dbus - Enable dbus support for anything that needs it (gpsd, gnomemeeting, etc)
debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
designer - Install plugin for dev-qt/qttools[designer]
geolocation - Enable position information via dev-qt/qtpositioning