Your socket is in blocking mode which means that you won't be able to write to it until your sysread in the thread times out--which it never will. The solution is to use Tye's method of setting the thread non-blocking

Update: made the listener detect when the other end disconnected.

#!/usr/bin/perl5.8.8 -w
use strict;
use warnings;
use threads;
use IO::Socket qw(:DEFAULT :crlf);

my $host = shift || 'localhost';

my $socket = IO::Socket::INET->new(
    PeerAddr => $host,
    PeerPort => 'ftp',
    Proto    => 'tcp',
    Type        => SOCK_STREAM,
    Timeout  => 5
) or die "Couldn't connect to remote host: $@\n";

ioctl( $socket, 0x8004667e, \1 );

my $listenerThread = threads->create(\&listener, $socket) or die "$@\n
+";

while (<STDIN>) {
  chomp;
  print $socket $_, CRLF;
};
exit(0);

sub listener($) {
    my $s = shift;
    my $data;
    $/ = CRLF;
    while( 1 ) {
        ## try to read something.
        my $read = sysread($s, $data, 2048);
        
        ## Quit if sysread gave an error (returned undef) other than 1
+0035
        ## 10035 =>  A non-blocking socket operation could not be comp
+leted immediately
        last unless defined $read or 0+$^E == 10035;
        
        ## If there was nothing to read, sleep a while and retry
        sleep 1 and redo unless $read;
        
        ## Got something, so display it
        syswrite(STDOUT, $data);
    }
    print "\nListener exiting\n";
};
__END__
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