More Helpful Error Messages for Unmount

Sometimes, when I try to unmount a USB drive or DVD, I get this message:

Cannot unmount volume
An application is preventing the volume from being unmounted.

Well, that's fine, but...*which* application? It doesn't tell me that, so I have to just click around, closing stuff, until I find the right one.

Will this error message be more helpful in the future? What can I do in the meantime to determine what applications are tying up my devices?

you might want to use lsof in the terminal. It lists open processes and might tell you what is tying your USB stick.