Thanks, I didn't know about QTabBar. That's one of the problems that I have with Qt Creator which is that the Design mode doesn't give access to some widgets and QTabBar is one of them...
Regarding the design itself, having mentioned Qt Creator above, I am obviously familiar with it. I don't, however, fancy buttons for the modes or, rather, not in the way it has been done in Qt Creator. They take too much space (and the more space I have the better), hence I thought of using some sideways text. Should that sideways text be a button, a tab or whatever doesn't really matter to me, as long as it takes as little space as possible.
As for the list open files, the issue I have with this is that once again it does take a lot of GUI space, especially if you have only a handful of files open (which tends to be the norm for the kind of application I am working on). In fact, another similar application I was working did it that way and people complained about it for the reason I just gave. Hence, it was thought best to have a QTabWidget in r0c1.
Anyway, I am still testing things, so will see how it goes...