One way of doing this is to calculate an id off of (say) the current UNIX time, plus maybe the first 3 letters of their first name plus the first 3 letters of their last name

Better yet, use the process idea (handily stored by perl in the variable $$) along with the time (stored by perl as $^T - the time the script started). Using this two ensures for a pretty unique string, since you can't have two processes with the same PID running at the same time.