We use Qt at work for closed-source development on Windows, although I'm the only person to use it cross-platform. As a former non-C++ programmer I found the API easy to use and I've written quite large applications surprisingly quickly. I've also been able to port these apps over to Linux with practically no changes, the Mac version seemed a little buggy. Although considering we don't seem to see eye to eye on things maybe you should take my comments with a pinch of salt.