Don't, it's wrong.

86400 seconds sooner/later can be the same day.
86400 seconds sooner/later can be two days earlier/later.

use DateTime qw( );

my $today     = DateTime->today( time_zone => 'local' );
my $tomorrow  = $today->add     ( days => 1 );
my $yesterday = $today->subtract( days => 1 );

print "Today is:     ", $today    ->strftime('%m/%d/%Y'), "\n";
print "Tomorrow is:  ", $tomorrow ->strftime('%m/%d/%Y'), "\n";
print "Yesterday is: ", $yesterday->strftime('%m/%d/%Y'), "\n";
[download]

Update: Added solution.
Update: Fixed spelling of time_zone. (underscore was missing)

In which case, we can use a CPAN module, such as Date::Simple:

use Date::Simple ('date', 'today');
my $date = today();
print "Today is: "     , $date, "\n";
print "Tomorrow is: "  , $date + 1, "\n";
print "Yesterday is: " , $date - 1, "\n";
[download]

Update: oops... didn't see your updated code

cool! doing the following now:

$today_tmp = DateTime->now();
$tomorrow_tmp = DateTime->now()->add( days => 1 );
$yesterday_tmp = DateTime->now()->subtract( days => 1 );
$today = $today_tmp->mdy('/');
$tomorrow = $tomorrow_tmp->mdy('/');
$yesterday = $yesterday_tmp->mdy('/');
print "Today: $today -=- ";
print "Tomorrow: $tomorrow -=- ";
print "Yesterday: $yesterday -=- ";
[download]

Works perfectly!

No, it doesn't. I thought you wanted the local date, not the date halfway around the world. If so, you introduced a bug by removing time_zone => 'local'. (Yeah, I had it misspelled.)

I'm also curious as to why you changed from today to now.