I don't know about Gtk/Qt, but the 4/5 change is a difference, not a breakage: the N900 comes with a stylus, so your Maemo 4 stylus apps will work fine. Think

I don't know about Gtk/Qt, but the 4/5 change is a difference, not a breakage: the N900 comes with a stylus, so your Maemo 4 stylus apps will work fine. Think of it as pre-notifications vs notifications vs limited backgrounding functionality changes on iOS. The older apps still work fine, they're just not taking full advantage of the newer features.