It's easy to monitor the behavior of require/use in your script. For instance, this script will run another Perl program and print out whatever files it's loading to STDERR:

#!/usr/bin/perl -w
my $db = <<'EOF';
sub DB::postponed {
  my $glob = shift;
  $glob =~ s/.*::_<//;
  print STDERR "loading $glob\n";
}
sub DB::DB { }
EOF
($ENV{PERL5DB} = $db) =~ tr/\n/ /;
system($^X, '-d', @ARGV);
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Just run it on another program like this:

perl watchRequire.pl myProgram.pl arg1 arg2 2>required
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update: hmm... seems useful, so I put it into Code.