I've read it several times, the first time being in highschool and the most recent being a few months ago. As I get older I've read it with a bit more skepticism about the novelty of his overarching ideas and the rigor of some of his reasoning but I always find the book full of valuable ideas and interesting food for thought.
Did the people from the 70s forget how to read now its 2013? ;)
I was born in '79 so although I was alive in 70s I wasn't really part of the whole free love movement or anything :)
I'm not sure its even that popular of a book for that cohort... I mean its a philosophical novel, what's the size of that market ever been?
There are certainly some things addressed in the book that aren't as applicable in a modern setting but the main thrust of the book investigates the intrinsic value or quality of things - That should always be applicable to future generations.
I read it first when I was in my early 20s. I seem to re-read it about every 5 years. Though some of the language is dated, I find the philosophical musing important enough to take the time to refresh in my mind. Finally, the "me" that I bring to the book is different every time I pick it up for the next re-reading...which is to say, I find that I relate to the text differently over time.
I just tried to read it, and had to quit when it started spouting all the pseudo religious advice as fact, and as a replacement for scientific inquiry.
When I read it, I was a young teenager in the 2000s. It was engrossing and mind-expanding, though perhaps I was more interested in 70s ideas than most.