This was fun. For readabilities sake, download the code..
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#!/usr/bin/perl

@_=(shift,pop); # we take the first and the last element of ARGV which
+ contains the 
                # 4 argumants of 'Just another perl hacker' @ARGV is n
+ow ('another','perl')


$*={ ord"<" =>    # we create the hash $* with 1 key-value pair. the k
+ey is ord("<");
                  # the value is a reference to an anonymous array whi
+ch contains
                  # a reference to an anonymous sub.

                  # ord"<" is 60, which happens to be the default valu
+e for $=

                  # $& the string matched by the last successful patte
+rn match
                  # $. is the line number in the file we are reading. 
+As we are reading no 
                  #    file this is 0.
                  # $|,the output autoflush is 0 by default and is inc
+remented on the last line
    [ sub{
            printf "%s",shift;      # print the first argument passed
            join $&,@ARGV[$.,$|]    # join remaining elements in @ARGV
+ by $& which will be ' ' because of
                                    # the regex to be executed soon. A
+s $. is 0 and $| is 1 because of
                                    # the foreach on the last line we 
+are joining 'another' and 'perl'
                                    # together.
      }
    ]
 };



$\=(                    # $\ is the output record separator for print
     ($,)=$"=~?( )?     # by default $" contains a space
                        # it gets matched by ~/( )/ and put
                        # in $, which is by default a empty scalar
                        # also the result of this succesfull match is 
+put in $&

   ) 
   &&                   # if the match was succesfull 
   qq; $_[$#_]\n;;      # Perl evaluates this line which
                        # due to the assign to @_, $_[$#_] results in 
+' Hacker\n'
                        #
                        # If the regex wouldnt match the second part w
+ould not have
                # been exectuted.
                # Now if you print a list, it is terminated by ' Hacke
+r\n';

# Read the following section backward. Starting with 1, then moving up
+ to 3.
#
#

print+chop$,            # 3. The result of the function called in 2. i
+s in $_ and $, (a space) is chopped off,
                        #    the result of the chop function is printe
+d.
                        #
                        #    However, as the OUTPUT_RECORD_TERMINATOR 
+is set to ' Hacker\n'
                        #    the printed string is appended by this. (
+Note that the print in called
                        #    sub was actually printf
                            
,$*->{$=}->[$[]->($_)   # 2. $[ is first array index. By default 0 and
+ hasn't been reset
                        #    so actually we are saying:
                        #    $*->{60}->[0]->($_) (so we call $*->{60}-
+>[0]->('Just');
                        #    the return value from the called function
+ is 'another perl'

foreach($_[$|++]);      # 1. We return 'Just', as soon as element $_[0
+] is returned $| is incremented by 1.
[download]

Update: removed a mistake about $| not being modified in the program.