Sure: making geometric shapes and masks. A varient of diagonal borders is currently used in http://nicolasgallagher.com/pure-css-speech-bubbles/demo/ http://ni

Sure: making geometric shapes and masks. A varient of diagonal borders is currently used in http://nicolasgallagher.com/pure-css-speech-bubbles/demo/ http://nicolasgallagher.com/pure-css-speech-bubbles/demo/ The trick there is to use the CSS :after pseudo-element to get a triangular shape/mask, but it's a bit of a hack. Having diagonal CSS borders that were properly supported would make doing stuff like this much cleaner and easier to implement.