One of the banes of my existence! There's no place for these stupid effing banners when browsers have inertia scrolling and infinite-scrolling sites have fixed headers (or footers) visible all the time. Maybe I wouldn't be so frustrated if the tolerance for what makes a header reappear wasn't ~3px, which is what I often perceive it to be. It totally misunderstands human behavior, which isn't to read an article word by word all the way through like a robot but to reread things to better comprehend them and jump around an article to make sense of connected ideas.