The feature I've wanted for a very long time has finally arrived with Chromium v31; you can now inspect the :before and :after pseudo-elements within the Chrome DevTools! It is such a great quality of life change for anyone who spends a decent amount of time tinkering with CSS.
Previously you would have to find the pseudo-element styles within the styles of the parent, there would be no selection of the pseudo-element in the viewport and the width and height wouldn't display.