Skeumorphism and storytelling
tobiasahlin.com
tobiasahlin.com
That also accurately describes the importance of visual design overall, not just this one particular flavor of realistic-looking interfaces. It's what helps a product instantly "impute" what it's for, for those that read the Jobs book.
Straightforward UX will only get you so far and if functionality were the only thing people cared about, we'd all be driving Volvos and Ferrari would be out of business.
It's interesting to me that the riotously successful iPhone 4 has a somehow more familiar form than the iPhone 3. The Braun influence let Apple step out of a specific time and make an object that doesn't feel out of place on a Mad Men set.
http://30.media.tumblr.com/tumblr_m1w15nFNOH1qcuwbao1_500.jp...
It has a comfortable approachable familiarity, unlike the other plasticky gizmos at the mobile booth in the mall. These are known materials, glass and brushed steel, familiar to the touch, and emphasize the touchability of its OS.
Imagine Find My Friends with a standard grey/black iOS UI. User reactions would quickly go from 'this is neat' to 'this is scary.'
After using the interface over time, our perception of usability changes. I suspect, overtime skeumorphic design will lose its appeal overtime because many constraints will be forced on the user artificially. Flipping pages on the iBook may seem more work than just tapping.
The example that wanders into dangerous territory, though, is the desktop version of Photo Booth. While all the others I've mentioned serve to suggest what the app can do, Photo Booth's gaudy curtains-and-wood-paneling design dictates what you should do. It limits the range of the software's potential uses; the old grey photo booth was clearly a program for taking photos of anything you wanted with your front camera, while the new version is more apparently only for dicking around with your friends and taking silly distorted pictures. The skeumorphism of Paper serves to make the app more intuitive; the skeumorphism of Photo Booth serves only to constrict.
It's "invisible" and therefore well designed - it puts the Apps in front. It removes the "abstraction layer" of pointing devices, and if you watch a kid or grandparent interact, you'll notice how the non-mouse-indoctrinated respond far more intuitively.