well, according to the benchmark:

#!/usr/bin/perl -w

use strict;
use Benchmark;

my $x = "a b c d e f g";

sub list_context {
        my $y = (split(/\s+/, $x))[0];
}

sub extra_argument {
        my $y = (split(/\s+/, $x, 2))[0];
}

timethese(-3, {
        "LIST CONTEXT"  => \&list_context,
        "EXTRA ARGUMENT"        => \&extra_argument,
        });
[ed@darkness ed]$ perl ./splittest.pl 
Benchmark: running EXTRA ARGUMENT, LIST CONTEXT, each for at least 3 C
+PU seconds...
EXTRA ARGUMENT:  2 wallclock secs ( 3.14 usr +  0.00 sys =  3.14 CPU) 
+@ 115563.69/s (n=362870)
LIST CONTEXT:  3 wallclock secs ( 3.18 usr +  0.00 sys =  3.18 CPU) @ 
+57053.46/s (n=181430)
[download]

the extra argument version of split kicks the living crap out of not using it... so i guess, yes ;) it does make a difference!