Unfortunately, many employers take advantage of interns and have them doing actual work duties, even working over 40 hours a week, all the while without paying them a dime. Just because you are willing to gain experience for free does not mean that you should be taken advantage of.
In order for an internship to be considered unpaid, six criteria must be met. Read about recent case in the news:
Blog: Intern Slavery reported at Hearst newspapers
Texas interns: Do you know if the FLSA applies to you?