I've been very satisfied with Qt on the mac. I've ported a couple of linux applications I use. They are not as good as truely native ports (MacVim is clearly more of a "mac" app then any Qt built application), but it gets basic things like menu bar at the top and shortcuts using command instead of ctl right.

It's meh. Not as bad as GTK+ by a long shot but still a far cry from native applications. And OSX users generally don't like non-native applications (for a number of reasons)

Nothing, Nokia has come along way with it. It the latest (Qt 4.7.0) they are slowly getting things closer and closer to native look and feel. There are carbon and cocoa versions for the mac. The Cocoa version obviously integrate better than the carbon version will. There are also Qt classes to integrate Qt based widgets into cocoa based containers etc. Is it perfect, not even close. Is it pretty darn good, yes.