I was inspired by the idea that you can make a wide range of shapes using only CSS on a single div after reading this css-trics.com page. I created the Facebook Icon using a single div:
border-bottom: 20px solid #6d84b4;
border: 15px solid #fff;
It works in Firefox 5, Chrome 13, and Safari 5.1. It works in IE8, but the “f” is not rounded. See the JS Fiddle version.