It might be nice to have an option when right clicking on an entry in the now playing list that would be "Find in Library . . ." that could have flyout options of track, artist, album, genre, etc. I suppose this could also be an option under the "file" menu of the now playing list. The way Winamp handles this (via a third party plugin) is by automatically filling in the query box with the respective tag of the file right clicked to find in the library. I imagine for radio streams or podcasts, it might take you to the either the saved radio stream in the radio library or the particular podcast in the podcast library. For last.fm streams, I guess a message could indicate it's not in the library, or it could open a browser tab in the content pane with the last.fm page for the track, artist, album, genre, etc. (whichever is selected).
While I'm talking about additional tabs, it might be nice to have a new tab button just to the right of the bookmark button at the top of the content pane. I keep forgetting about using tabs and they could be quite useful so that I don't loose settings in such things as the Auto-DJ, etc.