In no perticular order:

Crash proofing - some done, some actions still unstable
Add more on screen instructions - options menu, status bar updates, tool tips
Progress bar
Fixed size for the grid resize widget
Match to style guidelines - code didn't before so I continued the style of each file for easier reading on a file to file basis
Check cross compatibilty with OSX and X11
Find a better way to cache the features between extractions so that a file is only extracted once
Have the four main functions (extract, train, init, predict) be able to be started from saved data (ie the saved feature hash curently)
Support for colouring other then the genres set. - iTunes data is a good start