Oh... "£$X%&... solved this one as well! I've two layers in my scene that I set up so to restrict the selection of the objects assigned to them. I dunno why, but any newly created object is now automatically assigned to one of this layers. Can someone at least explain the reason for this... just to know!
And... since I'm here ... could you please adivise about a good tutorial, guide or indepth analysis of the Hypeshade functions of Maya? I think the attribution of materials in Maya is very complex... at least to a newbye like me! Too many options and settings that make your navigation in this part of the program anything but easy...