I haven't had the opportunity to use Net::LDAP yet, so I will comment on the rest of the code.

Instead of printing line by line, why not use a here-doc for your usage message? Or use Pod::Usage and document your script in POD.

The following might make your defaults stand out more:

my ($user, $pass);
my $host  = 'yourserver.yourdomain.com';
my $port  = 389;
my $debug = 0;

GetOptions(
    'h=s' => \$host, 
    'p=s' => \$port, 
    'u=s' => \$user, 
    'w=s' => \$pass, 
    'd+'  => \$debug, 
    'q'   => \&usage
);
[download]

Often, things like if ($debug ne 0) { ... } are better written as if ($debug) { ... }.

I would write debug and status messages to STDERR instead of STDOUT and include $0 (or similar) in error messages.

Hope this helps.

— Arien