Do you ever have a list of items (such as a ul) in which each item is floating to make them appear side-by-side (an example is the list of sites at BlizzardDigital.org)? Tired of using a non-semantic, empty div after the ul to clear the items? A useful trick is to add float: left; to the ul itself. This fits the ul‘s box around its inner items. Without float specified, the ul‘s box does not wrap around its items at all, making everything on the page after it scoot up behind all the list items. Very annoying. The normal fix for this would be to make the following element clear, but this isn’t always desirable. Your options are probably to have an empty div after it specifically to clear it (yuck) or make the probably unrelated following element clear it (yuck also). Just float the containing element (in my example, a ul) and set its width to 100%. The width makes sure no one squeezes in on the sides and therefore no clearing is necessary.
Clear as mud, right? 🙂