We recently got a new dog, after being being dogless for a few years, and one of the first things we bought was a Kong. I remember them as indispensable. Fill them with treats and/or peanut butter, and it would keep our pit bull busy for at least an hour. We would get a good six months of use out of before we might start thinking about replacing it.
That's what I remember, at least.
Hear is a picture of our current Kong, after only 1 month of use.