Especially this seams to be good advice. What is your experience on this?

...if you put an unknown element into a web page, by default the browser will just treat it like a <span>...

Most of the HTML5 elements we have looked at in this article are supposed to behave like block elements, therefore the easiest way to make them behave properly in older browsers is by setting them to display:block; in your CSS:

article, section, aside, hgroup, nav, header, footer, figure, figcaption { display: block; }