Does it not support listening to music on http://www.last.fm/listen? Seems to only work when you listen to music on user's pages.
Also, it would be awesome if this script could notify you about what a user is listening to (Recently Listened Tracks). That way I could listen to music on Spotify, link it to my last.fm account, then be notified every time the song changes, thus working as a Spotify notifier too. :)