It's a shame how far GTK is falling behind. From a user's perspective, I liked GTK2's smooth, clean interfaces much more than anything made in Qt, so much that I didn't even mind putting up with its insane APIs.

But now? GTK3 interfaces are horrible from an user's perspective – client-side decorations are a sin that we should know better than to repeat, plus a whole load of changes just for change's sake to spite users (the file chooser dialog has a much worse UX; mouse wheel support was widely gutted because apparently I'm supposed to want touch interfaces instead?) –, and the APIs are still as bad to use, most changes seem to have been made out of spite; a small shim would have allowed most programs to switch from GTK2 to 3 without code changes, had it not been for those.

Now I find myself increasingly switching to Qt programs. While the interfaces are still somewhat rougher than GTK2 ones and not as unified, it still beats GTK3 crap. That seems to be turning from "a reasonable toolkit for all X11 invironments" into "the official Gnome 3 toolkit, beg us if you want interoperability".