Amusing stuff ++.
I thought it might be fun to make the subroutine a little less clear:

use warnings;
use strict;

for(1900, 2000, 2100, 2200, 2300, 2400, 1964, 1965, 1966, 1967, 1968) 
+{
   print "$_\n" if is_leap_year($_);
}

sub is_leap_year {
  my $year = shift;
  return !($year % 400) || $year % 100 && !($year % 4);
# Or:
# return !($year % 400 && !($year % 100) || $year % 4);
}
[download]

I hope it's correct, at least.

Cheers,
Rob