Lots of code in QMainWindow

[wysota]

I create a seperate UI file for each tab, place a QWidget for each tab on the main form as a holder, and then tab->SetupUI(Widget). No promotion or subclassing necessary, and the source code and widgets for each tab is completely seperate.

Please don't do that. You'll encounter more problems with it than benefits. Make proper subclasses from those widgets and either use the promote facility of Designer or add tabs to the tab widget manually. It's really worth it. Otherwise once you start writing some code logic you'll again have everything in one file.