Windows Phone 7 is a brand new, and wholly re-worked user interface from Microsoft. It is based on Tiles, Hubs, and constantly-refreshing content that makes up the home screen.
Users can change the lay-out of the home screen to suit their own needs, and populate it with any number of tiles, each with its own application, shortcut or live information. In fact, Microsoft calls them "Live Tiles." No one was able to say how many tiles can fit onto the home screen.
The tiles are laid out two-by-two in a lengthy column that stretches down the screen. Flicking up or down sends the home screen zipping in either direction. Swiping the main menu to the left opens a single-file list view of all the applications and settings. It is a long list, but you can scroll up and down quickly. Thankfully, it is arranged alphabetically.
Press any of the tiles, and the whole UI folds over to the left and offers short text menus with rich images/graphics. It's a little animation heavy. It looks nice, to be sure, but it might get tiresome over time.
Some of the apps let you continue to swipe sideways to access more content and menus, depending on which app it is. The Pictures, for example, offers different photo albums that can be accessed by swiping sideways.
The Hubs are the major organizational themes of WP7, such as People, Office, Pictures, Music & Video. Each of these is a department unto itself wherein lies all the associated apps, settings, and content related to that feature.