I know you're just tossing that code off quickly, but I'm curious to know why you chose to write:

while (<>) {
  my ($f) = (split)[6];
  $count{$f}++;
}
[download]

...rather than...

while (<>) {
  $count{(split)[6]}++;
}
[download]

It makes me wonder if there's some robustness principle at work that eludes me. And of course, there is even...

$count{(split)[6]}++ while <>;
[download]

... but then we are getting into the realms of the cryptic, and I don't seen a more concise way of printing the top N values that doesn't sacrifice economy.