Thanks for the pointers -- I finally got it, but it's a little messy:

use Mail::Internet;
use Mail::Address;

my @mail;

while(<>) { push @mail, $_; }
#read mail from STDIN and put it in @MAIL

my $EMAIL = new Mail::Internet([@mail]);
my $header = $EMAIL->head();
my @hlines;

push @hlines, $header->get('To');
push @hlines, $header->get('Cc');
push @hlines, $header->get('Bcc');
#thanks [ZZamboni]...

my @addr;
foreach (@hlines) {
  my $line = $_;
  $line =~ s/^\w+\:(.*)$/$1/gs;
   #this is necessary to cut off the initial "To:" from the
   #header line -- I'm not sure why Address::Parse doesn't
   #do this
    
  push (@addr, Mail::Address->parse($line));
}

#we now have a list of address objects -- convert to text addresses
foreach (@addr) { $_ = $_->address }

#our addresses are now in @addr
[download]

if anyone has any suggestions to tidy this up, please post. Esp. clipping the "To:", "cc:", and "bcc:" seems like it shouldn't need to be there -- but this worked on my test emails.