Optimize existing term lookup

Instead of this sql query

  $sql = "SELECT * FROM {term_data} WHERE vid = %d";
  $result = db_query($sql, $vid);

  // Look for a term with the same name based on case-sensitivity preferences
  $case_sensitive = variable_get('taxonomy_dupecheck_case_sensitive', 0);
  while ($found_term = db_fetch_object($result)) {

    // Skip the check if the current found term is the same term we're comparing.
    // This will happen on updates to an existing term.
    if ($tid == $found_term->tid) {
      continue;
    }

do sg like this:

  $sql = "SELECT * FROM {term_data} WHERE vid = %d AND name = '".$term."';
...

There is no need to get the entire vocabulary. Just check if we have a record.