How about something like this:

my @regex = qw( Desription Data );  # regexen to match
my %rhash = ();

my $which = 0;  # which regexp to look for

while (<>) {
  /^$regex[$which]:/ && do {   # found one of them
    if ($which == 0 ) {        # if it was the first one ..
      # process Description and Data arrays (if any)
      process_arrays( @rhash{ @regex } );

      # reinitialize by associating an anon array with each  regex
      @rhash{ @regex } = ( [] ) x @regex;
    }
    $which = 0 if (++$which >= @regex);
    next;
  }
  push @{$rhash[$which]}, $_;
}

# Since the last Data block won't be terminated with a
# Description line, need to cleanup here
process_arrays( @rhash{ @regex } );


# ...

sub process_arrays {
  my ( $arrayref1, $arrayref2 ) = @_;
  # return immediately if both arrays are empty
  return unless $arrayref1 && @$arrayref1 && $arrayref2 && @$arrayref2
+;

  # ...
}
[download]

Update: Oops! my first version was plagued with Off-By-One bugs. This should work (untested).

dmm