わざわざスクレイピングせずに XML::RSS とかCPANモジュール使えば?

#!/usr/bin/perl
use LWP::Simple;
use XML::RSS;

my $hatena_id = "Marathon";

my $rss = new XML::RSS;
$rss->parse( get("http://b.hatena.ne.jp/$hatena_id/rss";) );
my $items = $rss->{items};

my %count;
for my $item (@$items) {
  my $item_rss = new XML::RSS;
  $item_rss->parse( get("http://b.hatena.ne.jp/entry/rss/$item->;{link}") );
  $count{ $_->{title} }++ for (@{ $item_rss->{items} });
}

my @ranking = sort { $count{$b} <=> $count{$a} } keys %count;
for my $user (splice @ranking, 0, 10) {
  my $per = $count{$user} / @$items * 100;
  printf "%.2f%%\t%s\n", $per, $user;
}