in reply to Reverse Dependency Usage
It depends on what you mean by use, and what universe of modules you want to test. All the modules in the lib path on your system? All the modules on CPAN?
If on your system, and If you are referring to compile time use you can write a script to use File::Find on your @INC path and require() every module found, then check %INC to see if your module is in there.
But those modules could still be dynamically loading the module, and that's a bit harder to test for.