The ribbon in AutoCAD 2010 enables you to interact with the user interface more efficiently than ever before. It provides many context-sensitive tabs that display the tools you need when you need them. For example, if you select an external reference, AutoCAD automatically displays the External References ribbon tab. If you select an attached image, AutoCAD automatically displays the Image ribbon tab. The same holds true if you select a PDF attachment (new in AutoCAD 2010), a DGN attachment or a DWF attachment.
In each case the AutoCAD ribbon displays the tools you need most for that selection. The ribbon is also context-sensitive when you’re editing blocks, text, meshes, in-place references, section planes, and tables.
On a completely unrelated note, have you responded to the AutoCAD 3D survey? We'd appreciate your input!