Currently, when you click to delete a movie in the web interface, you're presented with a list of the files if there are multiple copies of the same movie.
Unless I'm missing something, this screen is sort of hard to use, because it doesn't include the full name of all files and the size of them, which I would think would be the only way you can really make an informed decision about which files to delete.
I use the "Duplicates" movie filter to find duplication, and it's awesome, but from the results page, it's difficult to actually do anything about the dupes, because I've got to go back to my filesystem to see what it's talking about.
Kind of an esoteric feature, but it seems like the screen is already there, just slightly less useful than intended