The drag and drop functionality works (with an occasional odd weirdness, that I'm trying to solve). Whenever a note is dropped, the appropriate note and duration are produced (although, it's a bit tricky, because the Y value that marks the end of one note is very close to the Y value that starts the next note). The latter needs some fixing but is just a matter of repetition, no further investigation needed there.
The biggest gap in functionality is that, right now, you can't play the whole piece, i.e., all the dropped notes together. How I'm going to solve that is by having another topcomponent, below the palette, containing a text area, where a dropped note will output its related music string. All music strings together can then be played, by using the music notes in the text area, exactly as done in my initial implementation (described here).
Also, I'm going to add another section to the palette—for instruments! There'll be a handful of icons for basic instruments (not the 200 or so that the JFugue API supports) that can then be dragged before the notes that they will influence.
And why is it called "Music NotePad"? Well, it's supposed to make you think of "NotePad", which provides an absolutely minimal text editor. Don't want to raise anyone's hopes that this is going to be more than the absolutely bare bones implementation of JFugue API!
(Thanks to Talley Mulligan for fixing the icons so that their backgrounds aren't white.)