Application indicators are simple menus so it is easier and more consistent to interact with them than with the current notification area icons, where each icon behaves differently. Some are showing different popup menus on left and right click, others are showing or hiding some dialog/window on left click.

I started to add support for Application Indicators to gnome-power-manager, IBus and gnome-settings-daemon last week. Patches for upstream are also available (1, 2).