When markup changes from this:

<div class="article">
	<div id="header">Header</div>
	<div id="content">
		Content
	</div>
	<div id="footer">Footer</div>
</div>

To this:

<article>
	<header>Header</header>
	<section>
		Content
	</section>
	<footer>Footer</footer>
</article>

It makes for a very different looking CSS file due to a lot fewer IDs and classes. But after getting carried away initially and using only CSS3 selectors, scalability became an issue. So there are a few IDs and classes in the CSS, but still fewer than usual.