Back in 2009, Microsoft filed a patent application for the "page curl feature" – exactly the way it's implemented on the Apple's iPad. The iBooks iPad application has a page turning feature that replicates the curling of a page when you flip pages in a book.
Here's an excerpt from the patent application: “One or more pages are displayed on a touch display. A page-turning gesture directed to a displayed page is recognized. Responsive to such recognition, a virtual page turn is displayed on touch display. Virtual page turn actively follows page-turning gesture. Virtual page turn curls a lifted portion of page to progressively reveal a back side of the page while progressively revealing a front side of subsequent page. A lifted portion of the page is given an increased transparency that allows the back side of the page to be viewed through front side of the page. A page-flipping gesture quickly flips two or more pages."