As more and more interns are entering the workplace, either as paid or unpaid workforce, we need to know from a company standpoint and labour reporting how many interns are within organizations and for how long are they working. In addition to statistics it is important to keep track of interns as employees from a recruitment standpoint as sometimes interns are hired on afterwards as full-time employees. Your recruitment lifecycle should log how long it takes to hire an intern as an employee as well as the recruitment source (school).
Another thing to consider is the training and development costs from providing 'on the job' training to interns. Currently, the Ministry of Labour does not include interns, that are part of the recognized Colleges and Universities internship programs--hence they are not protected under the Employment Standards Act.
"This exception exists to encourage employers to provide students enrolled in a college or university program with practical training to complement their classroom learning."Source http://www.labour.gov.on.ca/english/es/pubs/internships.php
I look forward to hearing from other HR professionals if you record interns as an employee either from a statistical, legal or other reason.