Qt - GPL, yet restricted still
First, thankyou TrollTech for listening to the community. At the least, this will make including KDE in the Debian distribution easier, and will also encourage development in Qt.
However, I had two reasons for not using Qt. The license was a pretty strong reason, but the other reason is just as important. Language. Qt is too strongly bound to C++. I am a C programmer at heart, but I often use other languages when it's more appropriate. If I was to develop Qt apps, I would find myself almost certainly required to use C++. And so I still won't use Qt.
btw, there's a discussion on this, including information about a C binding, at http://qt-interest.trolltech.com/apt5.html. I found this by searching for "language bindings" on the www.trolltech.com front page. Go to www.gtk.org and look in the sidebar on the left, it caters to a very large number of languages.
As for Win32, there may well be a Qt port to it in fairly short order. There is a Win32 port of GTK+, for instance.
No, this is not about C vs C++, it is about choice, nor is it about GTK+ vs Qt, beyond why I chose GTK+, it is about my reasons for avoiding Qt despite the license. Open Source to me is about choice and freedom. (So use Qt if you like, and thanks TrollTech, for the freedom part of it.)