Can't separate collection into groups by first letter.
Filtering depending on the time you added a song to the collection. Back in 2.1
No support for PostgreSQL or Sqlite. Will not come back, we use MySQL (Embedded) exclusively now. Support for MySQL daemons will come in a later release likely. External MySQL server support is available in 2.2.
Media devices
Some media devices are not yet supported:
USB Mass storage: only via file browser
iRiver iFP, Creative Nomad JukeBox and Dell DJ digital audio players, Rio Karma
Playlist
Queuing in the playlist Back in 2.0.1
Stop after track Back in 2.0.1
Filtering Back in 2.0.1
Sorting based on different parameters. We have a plan for a new UI to do this, it will be implemented in a future Amarok release.
"Classical", table like playlist view Back in 2.1
Organising tracks from within playlist. i.e. no "move to collection" option.