I found out a few nights ago when I updated/installed the Battle.net launcher that they're using Qt (5.x?). I had a suspicion when I saw it because it just "felt" like a Qt app, so I looked through the copyright notices and sure enough...
I've always liked Qt for native apps. It's a little awkward to get used to at first (signals are awesome though!), but it's probably one of the best GUI toolkits I've had the pleasure of working with in a long time, and certainly the best cross-platform one (sorry GTK fanboys!).
And yes, Qt widgets are completely and easily skinnable. Should do that to my private server launcher!