A good example of this was brought up by Josh Clark in his talk at Swipe Conference a few months back: the Address Book app on the iPad. The main interface is an open book, but you can't swipe through pages like you're actually reading an address book. In fact, if you swipe in the middle of the right page, you're going to swipe on a contact's field and then a delete button will pop up! Trying to swipe from page to page (like you would if this design mimicked the real object's affordances) could actually be a destructive action.
The design of Classics for iPhone and, later on, iBooks is skeuomorphic and resembles an open book, but you can (mostly) treat the app as if you would a book using similar actions. This is an example of skeuomorphic design that actually works. It looks and works like the real world thing it's emulating.
Bad skeuomorphic design simply looks familiar, but the user experience takes a wrong turn as soon as you start to use it like you would use the real thing. Bad skeuomorphic design can actually deeply harm the user experience because it builds up a false trust with users.
However, using real-world textures, patterns and materials like leather, tartan, glass and aluminum in your app interfaces just to spice it up a bit does not necessarily mean you're designing in a skeuomorphic manner if these items are used purely in an ornamental sense. An app like Find My Friends that looks like a baseball glove obviously isn't made to replicate a baseball glove's functionality, it simply uses some stitched leather textures from the real world. This doesn't mean it's a skeuomorphic interface but it does, in this case, mean it's ugly. The secret is to use realistic patterns and textures sparingly, not drop them from the sky all over the screen.