I wished to download a number of MIDI files but when I added them to Synthesia looking through all the songs was overwhelming. Is it possible for the user to sort songs into folders and open/ collapse them?
If so ignore the following idea:
There could be a button on the song list that would switch between it's current view (which is excellent for sorting a-z and with difficulty level) and another view. This 'other' view could be styles like the old Windows drop-down/expansion thing. Not sure what to call it but it didn't have actual folders it had a little + sign next to the folder things name and when you pressed it, it then expanded to all the files inside the folder. I think this would be useful to find the MIDI files that you wanted. Also I'm not sure but I believe that Synthesia could use the same folder watching/file detection system to create the folders i.e. Easy, Medium or any user created folder that is in the file.
Anyways the program is awesome and I can't believe I haven't found it earlier. Just remember if this has been suggested this is my first post so be nice. =P
Possible my longest first post EVER.

Edit:
Nicholas,
I didn't want to say this and look stupid at first but now I've checked it out, I've never seen a developer/creator so involved with the community and so willing to make additions to the program. Usually there are suggestions boards but they are never taken into account. So in summary: You rock! =P