From the technical aspect this is well done because it shows the power of CSS. From a designer's point of view it is quite far from perfect. The icons look weird and the active state looks quite uninspired with only showing an inner shadow. We shouldn't over hype such things just because "there are no graphics used". The user doesn't care if there are graphics used or not. Also the user won't recognize a difference in loading time because the icons wouldn't weight many bytes.