Over a seven-year span, I utilised Qt on a few of C++ projects on various platforms.
I think it works fairly well, and it was certainly faster for me to construct a solid GUI software on the Mac than wading through a language I didn't know at the time (Objective-C).
I believe the signal/slot mechanism is a little strange, but it's not terrible.
It's hardly a show-stopper after a few minutes of use.
The connection stuff is simple to screw up (or was) and it's always a good idea to verify the return on those because your programme will go on its way without telling you that it didn't function.
I've never used jambi before.