If there's one thing all the current platforms have in common, it's their relative flatness. Whereas iPhones were initially full of realistic textures, knobs, push buttons, and so on, the modern platforms are much flatter.

During the transition to visually flat platforms, the prior platforms were often described as overly skeuomorphic. Apple's Game Center and Calendar apps were often paraded as excellent examples of this due to their felt and leather textures, respectively. While it served as a rallying cry, it is important to recognize that the modern platforms have not actually abandoned skeuomorphism—only the often over-baked textures that accompanied it.

A skeuomorph is simply a representation of a real, physical object; this helps users feel more at home when using the app. When presented with a knob, button, or switch, users know that it can be turned, pushed, or toggled, respectively. None of the modern platforms have abandoned these concepts. Furthermore, many app designs still feature skeuomorphs as well—calculator and calendar apps being prime examples.

Therefore, when designing your app, don't completely eschew skeuomorphism. When used properly, it can give your users instant insight into how your app works. Use it with care, however, an improper skeuomorph is perhaps worse than none at all.