This utility finds missed opportunities to use slot operators.

If you pass a list of cat/pkg-ver strings they will be checked.
If you pass no arguments the entire portage tree will be checked.

There is plenty of room for improvement here, such as identifying maintainers, 
etc.  Patches, push-requests, etc welcome.

Note that this uses portage to find dependencies and it respects the settings in 
/etc/portage.  That means that it will only find dependencies that aren't 
keyword or package masked, and you may want to override these as a result 
(environment variables work fine for this).