[liw]

Stderr should only get error messages, and, arguably, warning messages. It shouldn't get status and progress messages. Those should go to /dev/tty, and the program should be gracefully quiet if run without a terminal, e.g., from cron.

[restalis]

Shouldn't the "verbose" option take care of the presence of the status or progress messages? Also, arguably, the error and warning messages are status messages too, so I would say all the status messages, regardless of gravity, belong to the same channel.

[liw]

Error and warning messages are not status or progress messages, at least not in the context of this discussions, which is that a long-running computation should indicate to the user that it's doing something.