Introduction à HTML5. Graphics. HTML5 Demos and Examples. Periodic Table of the Elements - Josh Duck. C HTML5 Logo. When can I use... Support tables for HTML5, CSS3, etc. Icon Fonts are Awesome.
Because you can easily change the size Because you can easily change the color Because you can easily shadow their shape Because they can have transparent knockouts, which work in IE6 unlike alpha transparent pngs.
Because you can do all the other stuff image based icons can do, like change opacity or rotate or whatever. You'll be able to do things like add strokes to them with text-stroke or add gradients/textures with background-clip: text; once browser support is a bit deeper. Codrops - useful drops of code. Creative CSS3 Animation Menus. Ultimate CSS Gradient Generator - ColorZilla.com.