Maarten Struys has a two-parts blog post on Windows Phone Mango tiles:
Live Tiles have been one of the nice differentiators of Windows Phone. In Mango, Live Tiles even got better, as a matter of facts, way better for end users and for 3rd party application developers. Today, applications can benefit from multiple secondary tiles that allow deep linking into the application. With Mango, all tiles have a front and a back that can contain different information. On the home screen, tiles with information stored on both the front and the back side will regularly flip over to see both sides of the tile.