Trust me, I've written enough code in various languages and using various frameworks and toolkits to know that when you want stable, simple, reliable cross-platform code, Qt is excellent.
I was looking at Qt. The developer license is pricey but probably doable. What does it provide for the kinds of controls I mentioned? Do you know of any demo apps I can look at that illustrate how well they function?
As an example of the kind of app I'm thinking of, consider a model train control panel which can control the speeds of various locomotives and report track conditions in real time (eg. graphing the impedance of the tracks).
For an example of the kinds of controls I'm looking for, National Instruments' Measurement Studio is an instrumentation GUI control library:
<http://www.ni.com/mstudio/> And as you can see, there's no Linux port.