I wrote these about SequoiaView, but they apply to gdmap too:
texturing/colouring on age, depth into tree, size, different for each directory
block size based on age, other stuff
3D view - cubic media - squares reach into
Show a thumbnail on the filename tooltip
distribute tooltips - one at the top right corner of each parent directory for the currently selected file
arrows for symlinks
use magic to determine file types
keyboard navigation - between files on same map & into & out of directories & up to root & down to container
hard links - 2 way arrows similar to symlinks
block (buffered) special - texture
character (unbuffered) special - texture
named pipe (FIFO) - texture
socket - double arrow out into nowhere ?
when you double click on a file the mouse pointer is repositioned over the file you klicked on in the correct position
make subdirectories seem more raised?