I beg to differ...

For this substr based implementation it's important to have the temporary array @parts. For the regex it's unimportant! So if we leave the assignment to the array out, the regex is way faster!

Update: Can this be due to the fact that the functions might be called in a scalar context?

use warnings;
use strict;
use Benchmark qw(cmpthese);

my $str = "Just Another Perl Hacker";

print join " ", do_mapstr (), "\n";
print join " ", do_substr (), "\n";
print join " ", do_regex (), "\n";
print "\n";

cmpthese (-1,
        {
        mapstr => \&do_mapstr,
        substr => \&do_substr,
        regex => \&do_regex,
        }
    );


sub do_mapstr {
    return map substr($str,$_-3,3),(3..length $str);
}


sub do_substr {
    my @parts;
    
    push @parts, substr $str, $_, 3 for 0 .. length ($str) - 3;
    return @parts;
}


sub do_regex {
    return $str =~ /(?=(...))/g;
}
[download]

Result

Jus ust st  t A  An Ano not oth the her er  r P  Pe Per erl rl  l H  H
+a Hac ack cke ker 
Jus ust st  t A  An Ano not oth the her er  r P  Pe Per erl rl  l H  H
+a Hac ack cke ker 
Jus ust st  t A  An Ano not oth the her er  r P  Pe Per erl rl  l H  H
+a Hac ack cke ker 

            Rate substr mapstr  regex
substr   25123/s     --   -48%   -97%
mapstr   48651/s    94%     --   -95%
regex  1003705/s  3895%  1963%     --
[download]