The Windows 7 (download) taskbar merges the quick launch and the task buttons into one single unified bar that reworks how you launch and restore applications.
The diagram above show three windows. Unlike Vista, which would only show a thumbnail preview for the active tab of the last viewed window, we worked closely with the Windows 7 team to give you previews of all tabs open in IE. Mousing over each of these previews will show you where (on any of your monitors) that instance or tab is located. (This “Peek” feature is also mirrored in Alt+Tab.) Clicking on the thumbnail preview will bring up the corresponding tab.
Full Article: IE Blog