Ubuntu – How to export all the mp3s from a playlist in Banshee

Try to enable the "Library watcher" Extension:

Edit -> Preferences -> Extensions

That, with the Organize music and folders option should do it, that's the way I keep my music organized automagically. You don't need to rescan the music library with this plugin enabled, if you drag and drop a file to the window or add it to the Music source folder set up in banshee then it gets added automatically.

I cooked one Python script quickly. You can review it here: http://db.tt/yGa14ZA or download from here: http://db.tt/Rnkhpod

As I understand your library is in MP3 format, so I used ID3 tagger. Script fetches last.fm top-tags and puts them in COMMENT tag.
If you ask me, although "TopTags" are more meaningful then "TrackTags" they can consist lots of garbage

Script uses Standard Python Library, except for module that writes tags - eyeD3 (sudo apt-get install python-eyed3)

Example usage (parse all files in current folder):

$ for f in *.mp3 ; do python lastfm_top-tags.py "$f" ; done

Similar bash line can crawl through all subfolders also.

Hope it's useful :)