I'm working on a file management system, written in Java (Swing). You know the sort of thing, icons, menu-bars, multiple windows, blah blah... The reason it's in Swing is so that it can be used on any system, and it should look the same.
Anyway, I'm looking for suggestions for useful features. Anything you've come across that you think should be included. The whole thing's going to be GPL'ed when it approaches usability, so it could be to your benefit.