I've absolutely noticed this. I generally don't remember what I read on HN, or in documentation. What I do remember is the fact that I've read it, and a vague sense of where, and hopefully a few keywords to type into Google. I actively try to keep my memory sharp by doing recall exercises, but I think it's a losing battle: when we know we can find something later you either consciously or subconsciously do less effort to remember it.