QT has been around for a while, It transferred hand from Trolltech(the first time I used it) to Nokia and now to Digia.
The recent project which I did on QT is create a gui based on C++ codes for computing chemical combinations for fluid dynamics experiment, which would takes hours to compute if done by hand and which was deployed in Linux system. The advantage of QT is the fact that the same codes can be used to deploy everywhere, in all platforms including Linux, Windows, Mac and other mobile platforms, with the powerful backbone of C++ or python.
The re-usability of code and rapid deployment, and at the same time the community version being free to use, makes it an attractive platform for development of engineering tools.
Software such as VLC player, Mathematica, Google Earth, Autodesk Maya etc are created using QT. Major corporations like European space agency, Dreamworks, Lucas Films, Philips, Volvo among many others, use QT for varied application.
Watch the video of a startup from oxford that uses QT:
[Image source for featured title image and video source: http://www.qt.io ]