I am also working on Qt only , previously worked on C# and ASP.NET , Also a certified MCTS (Application Development Foundation 2.0) and MCTS (ASP.NET Application Development 3.5) n now looking forward for Qt certification.
Its about 40%
the other parts is maintaining projects on VB and C#
but now we are focusing on multiplatform projects, and i think the Qt percentage will be grow.
~10%
But again, it depends. Half a year ago I was working 100% only with Qt.
Currently I'm mostly using C# ( Mono) and asp.net and a lot of SQL. From time to time php and Java if I really have to.
Currently I'm using Qt only for personal projects.
90%. When I find code examples that aren't Qt and I don't want to use them for web development, I always start the process of converting the code to use pure Qt. The only other development I do is occasional html/java/php development on websites.