I think your results are so surprising because your benchmark code adds a lot of unneccessary cruft to the different approaches. For example, in method 1 you're instantiating my $file at every pass through the loop.

FWIW, here's my benchmark of approach 1 (iterative) vs. approach 3 (slurpy):

use Benchmark qw/:all/;

my $folder = "C:\\Perl";

sub iterative {
    opendir $DIR, '.';
    my $file;
    while ($file = readdir $DIR) {
        $file = "$folder\\$file";
        next unless -f $file;
        my @s = stat $file;
    }
    closedir $DIR; # I like being explicit;
}

sub slurpy {
    opendir $DIR, '.';
    my @files = map { "$folder\\$_" } grep { -f $_ } readdir($DIR);
    foreach (@files) {
        my @s = stat $_;
    }
    closedir $DIR;
}

cmpthese ( 200, {
    'iterative' => \&iterative,
    'slurpy'    => \&slurpy,
});

__END__
            Rate    slurpy iterative
slurpy    74.4/s        --      -44%
iterative  133/s       79%        --
[download]

As you can see, the iterative approach is *much* faster in my benchmark. (The other variable is that I'm running WinXP). I have similar results on OSX (FreeBSD-based "Darwin"), see below.

C:\>perl -v

This is perl, v5.8.6 built for MSWin32-x86-multi-thread
(with 3 registered patches, see perl -V for more detail)
[download]

My test on my home OSX machine:

            Rate    slurpy iterative
slurpy    1264/s        --      -17%
iterative 1517/s       20%        --
[download]

$ perl -v

This is perl, v5.8.6 built for darwin-thread-multi-2level
(with 2 registered patches, see perl -V for more detail)
[download]

Updates:

• 2005-01.Jan-17 : OSX info added