In the Web client, you can set your mood to one of the defaults from the popup menu, and then type a custom label into the Other box. This has the effect of assigning the mood icon from the mood you selected from the menu, while displaying the text you chose to type in.
For example, you could choose "happy" from the menu, and then type "incredibly fantastic super wow" into the box, and your entry would appear with the "happy" mood icon alongside your custom text. In iJournal, the custom text simply appears without any icon.
It'd be nice to have this functionality in iJournal, as well.