I had the same issue with the Maplex extension, thanks for posting! Its not intuitive for me since I am currently using 9.3.1 and do not have the toolbars/extensions options. I just figured because I couldn't see Maplex or 3D Analyst under Customize -> Toolbars it wasn't installed but when I tried to go back and re-install the 'missing pieces' they were already installed.
Is this the case in version 10, too?