I haven't compared what this does with the actual Perl portability recommendations, but this seems to be a worthwhile addition to an author's quality (or kwalitee?) assurance toolkit. It's very simple to use.
UPDATE: it's occurred to me that there are some (minor) issues that it doesn't test for. Suppose::You::Have::A::Long::Module::Name, well, each subdirectory is under 32-characters so it passes tests, maybe t/Suppose-You-Have-A-Long-Module-Name.t fails the test but it's easy to rename that to a short name, you you still have it all in a folder called Suppose-You-Have-A-Long-Module-Name-0.123 or whatever that the current version of Test::Portability::Files doesn't test for.
However, I'm not sure it really matters since the limit pertains to "MacOS Classic and old AmigaOS", which should be an option like MSDOS and removed from default tests.
I'm also not sure if it tests for the maximum pathname lengths of Windows 9x or maximum directory depth and length of ISO CD-ROM directories.
But these are easily fixable issues, so shouldn't detract using it.