Are unpaid interships illegal ?

I see postings like this regularly on the job boards, UNPAID internships that aren't specified for students or even recent grads.

Essentially, "Work for us for free and we might hire you on our next gig - but we might not." Companies love interns for many reasons: a few are quoted from former "interns" who responded to posts, took jobs and were paid nothing.

1. You're free so they have an opportunity to make more money from your sweat.
2. You're off the books.
3. There is no paper work.
4. There is no government filing.
5. There is no proof that you even exist.
6. This is equal to tax evasion.
7. There is no employment tax.
8. They know you are financially frail, so you are probably not a legal threat.
9. It is easy to take advantage of you.
10. They can generally get you to use your car as if it belonged to the company and in that case, they have no vehicle insurance to pay and no driving liability. If you are involved in an accident, they don't have to even send you a balloon.

KNOW THE LAW!

http://laborlaw.typepad.com/labor_and_employment_law_/2007/11/unpaid-internsh.html
http://www.scrippsnews.com/node/23795
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/05/27/BUG0RQ19531.DTL

Don't devalue yourself in any industry by working for free.