I keep hearing this point brought up, but I haven't seen a good case for flat widget elements being confusing. In this very form I'm typing in, all the clickable elements (hyperlinks and submit button) are flat, but different styles immediately distinguish them from non-clickable elements, even if these styles vary between web pages and browsers. It's never been the case that GUIs consistently used 3D appearances to denote clickable widgets. 3D elements add a lot of visual clutter for complicated interfaces, which is why those "flat UI sucks" posts only show <10 GUI elements side-by-side. Google "Word 95" and "Word 98," both have a flat menu bar, though Word 98 has the addition of flat toolbars which helps readability.