Simple hover effects created with CSS filters. CSS3 filters are currently supported in WebKit nightlies. Hence the walkthrough only uses the -webkit prefix for applying the filter effects.
By default the images have the filter applied. Hovering disables the filter taking the images to the default state in a smooth transition.
This is a pretty cool example for using CSS Filters as design effects. As an added bonus, the demo is an automated player that builds the code as you watch! Cool!