When you have 2 nautilus windows overlapping, but you want to drag files from
the top one to the bottom one, you currently have to drag the top window to a
place on the screen where the other window is suitably visable so you can drop
the files there. this makes the process of moving files more difficult.
if i have a folder called Music open and it's above a folder called My Files,
itd be cool if when i clicked and dragged some files in music, if the other
window(My Files) slid out from under neath "Music" so i could drop the files
there. the "My Files" window would slide back once the files had been
dropped(even if they werent dropped on the My Files folder).

I hope that was clear enough...i could do some mockups if more info is needed.