I think that many internships are a waste of time. That's just based on my own observations. Very often, when an intern comes in, nobody really bothers to give the intern any meaningful work to do. Why? Because they know that the intern:
(i) knows very little and therefore would need a lot of guidance to get the work done; and
(ii) would be leaving in a few months anyway.
So very often, I'd rather do the work myself, than ask the intern to do it. It would be quicker and more efficient. Time spent training the intern and getting him involved in significant projects is usually a bad investment of effort, because the intern would soon be leaving anyway.
My advice to interns is that if you really want to gain some actual valuable experience out of your internship, you either have to:
(a) pick a company that is known for running a proper internship programme (eg there are designated mentors; clear objectives set for what interns are supposed to do; a proper schedule of rotations etc)
(b) you have to really shine, be motivated, be interested, be likeable, be capable etc - so that other people will feel inclined to give you some meaningful work to do (even though they know you'll soon be gone).
Otherwise don't bother with the internships.