Make sure you get a copy from the 1930s! Everything else has been edited from the original text.
On another note, get a copy! I read it and was surprised a book nearly 80 years old is still highly relevant. It was actually pleasing to read the way people "spoke in books" back then as to today's book.
I think much better question is, which self-improvement books do HN recommend? I haven't read a lot of them but I'm planning on reading 7 Habits of Highly Effective People.
Has anyone actually read this book? Is it effective?
> How to win friends and influence people is 70 years old now.
Actually, it's 78 years old (2014-1936 = 78).
In any case, the book has been revised significantly. If you buy a new copy today, then you're not getting the 1936 text. Wikipedia[1] indicates that the most recent major update was in 1981.
> Have any other books on the topic been released that are highly popular?
That seems likely, although I doubt that any single book has had anything like the popularity of HtWFaIP (if only because HtWFaIP was published in a time when bookstore shelves were not overflowing with self-help books).
I'd be interested in an answer to this question, too.
[1] https://en.wikipedia.org/wiki/How_to_Win_Friends_and_Influen...