Apple's skeuomorphic design for iCal is bad. iCal has been made to look like a real calendar, but in reality it isn't used like a real one at all.
If iCal worked like a real calendar, skeuomorphism would have value, but in its current form, it's just an ugly skin. It doesn't actually show users how to use it.
By who's definition? Some common skeuomorphs are shutter sounds on cameras without physical shutters and page turn animations in e-books. These are both skeuomorphs because they reference functionality in an earlier object, and they are largely ornamental. However, these are also functional. The shutter sound tells the user that the picture has been taken, and the page turn animation provides a visual transition between two pages. Both of these could be accomplished other ways (such as a chime and cut-through-white respectively), but that doesn't make them entirely non-functional.
If iCal worked like a real calendar, skeuomorphism would have value, but in its current form, it's just an ugly skin. It doesn't actually show users how to use it.
Read about it here: http://arstechnica.com/apple/reviews/2011/07/mac-os-x-10-7.a...