In IE8, Microsoft introduced Tab Groups as a way to help you remember which tabs are related to each other. In IE9, you can drag a tab out of and between windows, use Windows 7 Aero Snap to compare tabs, continue watching a video while moving a tab, and pin a site by dragging a tab to the taskbar.
IE9 lets you fully focus on your websites as you drag a tab. Through hardware accelerated graphics and separate sessions for each tab, your tabs are fully and continually rendered, even while you drag a tab. If you're watching a video and want to move the tab or snap it to the side of the screen, in IE9, the video keeps playing as you move the window, making sure you don't miss a beat!