I've got a lot of experience with Qt, since I ported Google Earth from Windows to mac and linux, and it was Qt based back then. You have the problem of having slightly non-native feel because Qt has to code around platform differences to present a unified API. When we first released the app, we took a lot of criticism because of its non-native feel on all platforms (except for Linux, which doesn't have a native feel). So, if you want a top-quality app, you're probably breaking it apart into a platform independent core and then writing your interface separately on each platform using native API's. I wish that the cross-platform abstractions worked well enough to be indistinguishable from a native well-coded app, but we're not there yet.