[numo16]

Qt seems to be working alright for Autodesk Maya and Mudbox. They migrated the UI to it and everyone I've talked to that use these on various platforms don't really have any complaint about the UI (especially since they can use Qt, PyQt, etc... for building plugins).

[coffeaddict]

Also worth mentioning Qt Creator itself I would say.

[zanny]

And VLC, and Clementine, and Doomsday, Mathematica, Skype, and Virtualbox...

[mrpippy]

Mathematica has a Mac-native frontend, and always has. They've used Qt for the Linux/Unix frontend since 6.0, not sure if they're using Qt for Windows or not.

[pbsdp]

All of which are absolutely terrible looking applications with broken platform UX on Mac OS X.

[toyg]

Most of which wouldn't even run on OSX if they weren't written in a cross-platform GUI that dramatically reduces development times.

I'm sure the VLC guys would like to spend their days dealing with complicated video codecs rather than the craziness of yet-another-goddamn-GUI-platform.

[dman]

Also Sidefx Houdini