The monodevelop.com website just takes me to this "Xamarin Studio" thing that has severe restrictions on the usage of the free version, and pricing that's almost as bad as Visual Studio on the paid versions! Is MonoDevelop for Windows dead? All I want to do is develop a GTK# application without installing Linux!
There's still an .msi of version 3.0.6 up for download on SourceForge, if you really need version 4 you'll have to build it yourself.