Well this was pointless...Focusing attention on the platforms you natively support instead of a platform that doesn't even want you would make more sense to me.
As for one I see many usages that you may use like Gimp, Inkscape, or other small applications that are ported from Linux to Windows. If you are a devel at least to have a version of the environment to test on Windows. If you want to migrate .Net applications you may just use Mono and Gtk 3 and reboot. If you want to contribute a patch to Shotwell you can take the sources, compile them on Windows and do the patch. It would be silly to install an entire OS for just working on a small fix.
If you look at the push buttons, the GIMP ones are way too fat like in Gnome, and that can be seen in practically any GIMP interface window. There is more to actually matching a theme than matching just colors.
Also you can notice the misplaced triangle in the pixels button in the center of the GTK+ dialog.
Last edited by darkcoder; 10-29-2013 at 03:12 PM. Reason: typo
These 2 screenshots comes directly from the Wireshark blog. Again since GTK+ do not handle other non nix platforms as a first class citizen, you end up with gui's that looks as native as this on a Mac OS (sarcasm here, lol)
Instead, Qt looks like a real Mac app