not to mention that we are all worng regarding Aero but the term has been often replaced with real one so ... the truth is that Aero was name for new user interface, glass has nothing to do with it proof lying as early as Longhorn build 4039, the first leaked build that contained full working DWM Aero express, had Opaque (filled) window borders, but UI was still rendered via GPU while Aero (full) had Glass enabled next time this was seen in Vista beta 1 build 5112 if you install nVidia LDDM test drivers, you will be presented with again Aero Express and Aero Full but oh well ...