First, installing was a struggle. Annoyingly, the tests require Test::Perl::Critic, but this isn't listed as a prerequisite, causing the tests to fail. After installing that (and the honking pile of modules that it requires), the critic test fails on twelve out of twelve parts. Disappointing, considering that it's the most irrelevant part of the test suite.
Second, this module does not appear to function in its current form. Attempting to login with code copied straight from the documentation resulted in a terse "Unable to login" error message. Messing with the insides of the module to make it spit out some more information revealed this message:
Attribute (session_key) does not pass the type constraint (Str) with 'HASH(0x8e283b4)' at (eval 35) line 1
WWW::Facebook::API::REST::Client::Base::session_key('WWW::Facebook::API::REST::Client=HASH(0x88f149c)', 'HASH(0x8e283b4)') called at /usr/local/share/perl/5.8.8/WWW/Facebook/API/REST/Client/Auth.pm line 47