One of the nice things about Qt, in my opinion, is that they satisfy the needs not only of the F/OSS community, but also by the big dragons creating closed source software. They do this along the principle of "Quid Pro Quo", that is, if you make money without sharing your source, you need to pay. If you share your source we [Trolltech, which I'm not affiliated with] share ours for free.
Anyway, holders of commercial Qt licenses can do the same thing for their software. This is what
VCreateLogic just did with their
GCF framework. According to Prashanth, they
sold 13 commercial licenses in one month - congratulations!
I got to know GCF as a judge in last year's
QtCentre programming contest. It takes the abstraction one level beyond widgets and make it possible to build user interfaces using components. The cool thing is that you get a modern (albeit Microsoft-ish) look for free. And as GCF is dual licensed, you can try it out for your F/OSS project right now.