While I've never written any truly commercial software, Qt is without a doubt my favourite framework. In my previous job we had to write all our win32 apps using the native API, now Mr. Petzold did his best, but doing anything with it made me want to beat my head against a brick wall. Similarly I tried recently to get my head round Cocoa and found it very difficult to pick up.

Qt on the other hand 'just makes sense' to me. I get access to all sorts of libraries across so many different areas. I write code on my MBP at home and it compiles on the Windows and linux boxes at work. I'm sure if you want 100% integration with host OS or really whizzy performance then you probably need to go native. But that's never been an issue for me.