Has a file open. I would be nice to see that as a column in the lister.
Not sure how practical it would be, but it makes tracking down issues a lot easier.
As far as I know there isn't a good and documented way of getting this information.
Some of the SysInternals (now Microsoft) tools, like Handle.exe and Process Explorer, can do it but they don't reveal how and, last time anyone I know asked them, wanted to charge tens of thousands of dollars to licence the source.
There is one program with source on CodeProject.com but I gather it isn't reliable and/or only works in a limited number of situations. (I forget the exact details.)
If you know of a good method for finding the info then I imagine it would be added to Opus in one way or another.