Finding unique submission IDs

Here at my school, a lab is using drupal as their front end with a request form when people need some analysis done. The idea was to have a unique identifer for each submition since we will have repeat users and using their name or email isnt useful. I'm not a developer so I hacked up the webform module to include the following in the webform.module file:

function webform_help($section= "admin/help#webform") {
$output= "";
....
case 'webform/helptext#variables' :
$output = t('Available variables are: %username, %useremail, %site, %date, %uniqueid.');
....

and

function _webform_filtervalues($string, $strict = TRUE) {
global $user;

// Setup default token replacements.
$find = array('%username', '%useremail', '%site', '%date', '%uniqueid');
$replace = array($user->name, $user->mail, variable_get('site_name', 'drupal'), format_date(time(), 'large'), md5(uniqid(time(),true)));
....

We then use this unique id to identify and distinguish each submission.