Oddly enough the browser which most accurately renders all CSS codes at this time is the 3.5x version of upstart Opera. Features like background formatting and box positioning are still supported inconsistently enough for wary designers to want to avoid them, the more basic text formatting is strong enough to inspire you to take the plunge. The goal of CSS is to provide a way of separating content from formatting. The idea is to enable designers to use Heading tags and List elements again without having to sacrifice aesthetic control. Chances are you've probably formatted your page titles to stand out from the regular body text.
Most sites use different fonts in a larger size with a unique color for title text.
The real payoff comes down the line when you start creating different style sheets for different viewers. Combining browser detection with style sheets allows you to tailor your web site to individual browser needs without having to ever retouch the content. If your document is properly structured using Heading tags you can use style sheets to reformat and rearrange text according the capabilities of a viewer's specific browser platform. Your page titles can appear in big bold red and even move around and transform for viewers who have full javascript support while displaying in plain all caps for someone accessing your site from a cell phone. While this level of fine tuning is highly sophisticated it all comes back to properly formatting your raw content.