Why are you useing File::Find if you're not actually using it? Your code could be reduced a lot if you used File::Find, and your code would be able to safely handle symlinks and other operating systems.

If your behavior was a little simpler (relying on arguments instead of finding subdirs first):

use File::Find;
use strict;

foreach my $dir (@ARGV) {
   my $total;
   find(sub { $total += -s }, $dir);
   print "$dir: $total\n";
}
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Preserving the behavior of your script (mostly):

use File::Find;
use File::Spec;
use strict;

my $cur = File::Spec->curdir;
my $up  = File::Spec->updir;

foreach my $start (@ARGV) {
   my @dirs = &find_subdirs($start);

   foreach my $dir (@dirs) {
      my $total = 0;
      find sub { $total += -s }, $dir;
      printf "%-20s %d\n", $dir, $total;
   }

   print STDERR "$start: No subdirectories\n" unless @dirs;
}

sub find_subdirs {
   my $start = shift;

   unless(opendir(D, $start)) {
      warn "$start: $!\n";
      next;
   }

   my @dirs =
      map {
          -d "$start/$_" &&
         !-l "$start/$_" &&
         $_ ne $cur && $_ ne $up
            ? "$start/$_" : ()
      }
      readdir(D);

   closedir(D);

   @dirs;
}
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