That rule is good. Using divs normally is fine. However, it is possible to overuse divs. Sometimes you'll have a div nested inside a div (and so on) six levels

That rule is good. Using divs normally is fine. However, it is possible to overuse divs. Sometimes you'll have a div nested inside a div (and so on) six levels deep. That's considered bad. For example, <div id="div-holder"> <div id="inner-padding-div"> <div id="right-align-div"> <div id="centering-div"> <div id="actual-content"> is bad - you could reduce that to one or two divs at most.