You can go back to the old style of iTunes with the sidebar via View > Show Sidebar (Control-S, or Alt-V to show/open the View drop-down menu) - that won't make the menus always show, but the rest of the layout should then look similar to how it did on iTunes 10 with the left-hand sidebar
I just came on line to say that I had just found it too! As you say,top left hand coner there's a tiny icon that looks like an on/off switch and that it where the menus are hidden. I guess it made sense to someone in Apple! Got to wonder if they tested it with any lay people!