The moodbar returned as of Amarok 2.2.2. It shows you the "mood" of a track, which you can then use to figure out when something interesting happens in the song. In order for Amarok to analyze your music files to create moodbars, you will need to create moodbars using the moodbar program. (See the wiki for downloads and binary packages.) The moodbar package requires gstreamer and various plugins depending on the filetypes you use. You will not need phonon-backend-gstreamer.
The Moodbar has been entirely rewritten. There are two parts to the new moodbar implementation: the moodbar package, which contains a program that takes a music file and generates a .mood file, and support code in the Amarok source, which runs the binary and displays the moodbar. The moodbar package depends on the GStreamer libraries. Without the generated mood files, Amarok cannot show the moodbars for your music.