sorry juerd, can't agree. another common idiom that noone's mentioned is this:

sub do_stuff
{
    my $this = shift;
      my $session = shift 
           || die "Missing req'd Session argument";
      my $cgi  = shift || new CGI ();
       ...
}
[download]

aesthetics aside, here are some hard figures on efficiency (slightly reformatted):

[matt@dirty matt]$ ./test_arg_passing.pl
Benchmark: timing 2000000 iterations of 
argumentative_1arg, 
argumentative_3args, 
direct_1arg, 
direct_3args, 
shifty_1arg, 
shifty_3args...

argumentative_1arg: 17 wallclock secs 
(17.69 usr +  0.01 sys = 17.70 CPU) @ 112994.35/s (n=2000000)

argumentative_3args: 21 wallclock secs 
(21.93 usr +  0.02 sys = 21.95 CPU) @ 91116.17/s (n=2000000)

direct_1arg: 10 wallclock secs 
(10.86 usr +  0.04 sys = 10.90 CPU) @ 183486.24/s (n=2000000)

direct_3args: 13 wallclock secs 
(12.24 usr +  0.02 sys = 12.26 CPU) @ 163132.14/s (n=2000000)

shifty_1arg: 17 wallclock secs 
(18.07 usr +  0.03 sys = 18.10 CPU) @ 110497.24/s (n=2000000)

shifty_3args: 23 wallclock secs 
(23.91 usr +  0.01 sys = 23.92 CPU) @ 83612.04/s (n=2000000)
total: 42000000
[download]

not much of a difference, though the triple shift example is a bit pathological. here's the code for the above:

#!/usr/bin/perl -w

use Benchmark;
use strict;

package ArgTest;

sub shifty_1arg {
    my $this = shift;
    my $first_arg = shift;
    $$this += $first_arg;
}


sub shifty_3args {
    my $this = shift;
    my $first_arg = shift;
    my $second_arg = shift;
    my $third_arg = shift;

    $$this += $first_arg + $second_arg + $third_arg;
}

sub argumentative_1arg {
    my( $this, $first_arg ) = @_;
    $$this += $first_arg;
}

sub argumentative_3args {
    my( $this, $first_arg, $second_arg, $third_arg ) = @_;
    $$this += $first_arg + $second_arg + $third_arg;
}

sub direct_1arg {
    ${$_[0]} += $_[1];
}

sub direct_3args {
    ${$_[0]} += $_[1] + $_[2] + $_[3];
}

sub value { return ${$_[0]} }

package main;

my $total;
bless( my $object = \$total, 'ArgTest' );

my @args = ( 1 .. 3 );

timethese(
    2_000_000,
    {
        shifty_1arg         =>  
        sub { $object->shifty_1arg( @args ) },
        argumentative_1arg  =>  
        sub { $object->argumentative_1arg( @args ) },
        direct_1arg         =>  
        sub { $object->direct_1arg( @args ) },

        shifty_3args        =>  
        sub { $object->shifty_3args( @args ) },
        argumentative_3args =>  
        sub { $object->argumentative_3args( @args ) },
        direct_3args        =>  
        sub { $object->direct_3args( @args ) },
    }
);

print "total: " . $object->value . "\n";
[download]

matt