I don't think Qt is going anywhere. Of course, I'm biased--I use KDE, which is wonderful and uses Qt as the native toolkit. But that is an important point--Qt is used in a bunch of open source projects, and KDE itself is pretty big. I don't see Qt at much of a disadvantage to GTk even if it loses all corporate support.
Personally, I was not very impressed last time I tried to use wxWidgets. Unfortunately, this seems to be the best option for Haskell, and I really want to use an FRP style for my next project. Also, I suspect most of my problems were to do with my not knowing wxWidgets and using the Haskell bindings. (Particularly, I wanted a rich web view sort of widget, but that doesn't come in the standard distribution--the standard one just doesn't cut it.)
So: for most cases, I would advocate Qt over wxWidgets or GTk.
Personally, I was not very impressed last time I tried to use wxWidgets. Unfortunately, this seems to be the best option for Haskell, and I really want to use an FRP style for my next project. Also, I suspect most of my problems were to do with my not knowing wxWidgets and using the Haskell bindings. (Particularly, I wanted a rich web view sort of widget, but that doesn't come in the standard distribution--the standard one just doesn't cut it.)
So: for most cases, I would advocate Qt over wxWidgets or GTk.