I just whipped out an app today which has the UI entirely specified in QML (vanilla QtQuick code, not Cascades).
Originally Posted by app_Developer
It took almost no effort to handle both re-orientation, and the resolution differences between the PlayBook and Dev Alpha.
Out of maybe 10 hours of effort on the app, and after subtracting some time spent learning pieces of QML that weren't familiar to me (I've been learning it only about a week), I'd estimate no more than half an hour of that effort was solely dedicated to making adjustments related to those differences (essentially four different screen resolutions).
From what I've seen of Cascades, I wouldn't expect it to be significantly different in this area, so I have no real concerns about it.