Worth it or not, unpaid is often unlawful, and is a very bad sign about the company you're interning with. I can't tell you there's nothing valuable to be learned from bad companies, but don't confuse opportunities to learn with good places to work.
Being HN, I assume most internship seekers here are looking for software-related positions. Does unpaid even exist in this industry?
Also, the article mentions wall street many times. Most of the advice is for the banking/management/consulting field, so I don't even know why it's here.
My previous employer would get interns from the UCB Extension international diploma program. Since the students were not US citizens, the internships were unpaid, by law. But they were mostly placed into PM-type roles and such. The company did once post an unpaid database engineer internship, but I don't believe they ever filled it.