There are a couple of reasons I hand code instead of designer:
1) in Qt 4.x, the designer crashed on me with complex, multi page dialogs. I reported the bug and it is reportedly fixed in 4.x, but I am leery of relying on a tool that is potentially unstable.
2) IMHO, the code generated is rather ugly
3) I like to build on re-usable tools that make hand coding easier and faster
4) My app requires highly customized colors for everything and it is easier and better to build re-usable components by hand.