Intersection of installed packages with orphaned packages

[Stephen Birch <sgbirch@imsmail.org>]

I am interested in the intersection of packages installed on my
machines with the list of orphaned packages. This is to be sure
a program in use isn't orphaned without me becoming aware of it.
Ideally the program would be run from cron about once a week and email
a status report.

Is there a program already in existence that can do the check?

If it doesn't exist I'll write software to do the check, where would
be the best place for the program to acquire the list of orphaned
packages?

Steve