It is very common to set margin:0 and padding:0 as default to all HTML elements via the star hack.

* { margin:0; padding:0; }

And we get so used to explicitly setting margins and paddings to elements that require them, that we assume no padding & margins at all as default for all elements.

With html5shiv javascript, we can get most HTML5 functionality working in Internet Explorer (6,7,8). And with ie7-js, we can get IE (6,7,8) to behave more-or-less like IE9.
When using HTML5 elements such as header, section, footer, aside, nav, article & figure, the all star hack doesn’t work and hence we need to set them explicitly. (Looks like ie7-js is resetting the margins)

IE6 / IE7 :

IE8 :

margin:0 isn’t applied in IE 6/7/8. So don’t forget to set it explicitly for HTML5 elements.

header, section, footer, aside, nav, article, figure { display:block; margin:0; padding:0; }