A number of nice enhancements have been made to the Command Line. You can still have it docked at the bottom or top of the screen, and adjust the height to show previous lines. As always, click on any image to see an enlarged version.
Select the command icon to get a menu of recently used commands. This menu is also still available as a flyout on the context menu that displays after right-clicking the Command Line.
The enhancements I find most useful are those made to the undocked Command Line. I personally have never found much advantage in having the Command Line undocked in previous versions, but expect to be leaving it undocked when we move to 2013. When undocked, the Command Line shows a single line "floating" above the AutoCAD window. The width can be adjusted by moving the mouse to the far right side; when the cursor changes to the double arrow icon, click and drag to change the width. While a command is active, a user-seletable number of partially transparent lines of history (from 0 to 50) related to the active command will appear above the command line.
If you start a new command immediately after ending the previous command, the previous command's history lines displaying above the Command Line are replaced with the history of the new command. You can review the full command history by pressing F2 or selecting the up arrow icon at the right end of the Command Line.
The size of the full command history area can be adjusted by moving the mouse to the top of the area. When the cursor changes to the double arrow icon, click and drag to change the height. You can scroll the history area by using the mouse wheel or by moving the cursor to the right side of the history area to get the scroll bars to show.
If you move the Command Line near an edge or a corner of the AutoCAD window or docked palette, it will snap to it, and stay snapped in that position even if the AutoCAD window is resized or a docked palette is undocked. Here is the reason I will be undocking my Command Line: if you hold the CTRL key down when moving the Command Line, you can move it over the top or bottom of the AutoCAD window without having it dock. This allows you to position the floating Command Line over the left side of the Drawing Status Bar and reclaim the drawing space that the docked Command Line would have taken.
Select the wrench icon at the left side of the Command Line to display a context menu that allows you to customize the Command Line and also access the Options dialog.