cat /var/log/httpd/access_log | perl -l -a -n -e 'print $F[6]' | sort 
+| uniq -c | sort -n | tail -10
[download]

Hmm. A Useless Use of Cat, using Perl like it was awk, and then chaining together a few other tools like forking is free. Hmm.

I'd probably have written that as:

@ARGV = qw(/var/log/httpd/access_log);
my %count;
while (<>) {
  my ($f) = (split)[6];
  $count{$f}++;
}
my $n = 0;
for (sort {$count{$b} <=> $count {$a}) {
  print "$_\n";
  last if ++$n >= 10;
}
[download]

I bet mine runs with 1/4th the CPU.