Windows Sidebar: 'Sky's The Limit'

In some of the earliest builds of Longhorn, the Sidebar was the most visible change. While its eventual use within the operating system wasn't initially clear, its sudden disappearance in the build given to attendees of WinHEC surprised many Windows enthusiasts.
http://www.betanews.com/article/Windows_Sidebar_Skys_The_Limit/1126727539