++Perl Mouse!!!
this one works as expected:

#!/usr/bin/perl -w

use strict;
use Getopt::Std;

my $what;
$| = 1;
my @hosts;
my %opts;

while (<STDIN>) {
  chomp;
  push(@hosts, $_);
}

getopts(':dw', \%opts);

$what .= ' bla' if $opts{'d'};
$what .= ' blabla' if $opts{'w'};

print "OK? [Y|n]>\n";
open my $kb, "<", "/dev/tty" or die;
while (<$kb>) {
  exit 1 if /^[nN]$/;
  last;
}

print "Did not stop, sorry!\n";
[download]

Running it now looks like this:

$ echo -e "aaa\nbbb\nccc\n" | script.pl -d
OK? [Y|n]>
y
Did not stop, sorry!

$ echo -e "aaa\nbbb\nccc\n" | script.pl -d
OK? [Y|n]>
n
[download]

Thanks a lot for solving this!
Regards,
svenXY

ptum, I wasn't able to do it with seek - just out of curiosity - how would you do it?