The other day someone asked me about GMime on Windows and I didn't have anything to tell her other than that I thought people had built it successfully on Windows but beyond that, I didn't have any sort of VS project files or anything.
Then, last night, she poked me again asking for advice about some of the problems she was having building on Windows (which were mostly removing extraneous unistd.h includes from files that didn't need them and dropping source files that required them).
After a short while of back and forth, I decided I'd just boot into Windows myself and she helped me get my system setup (installing GNU Libiconv, grabbing the Gtk+ Windows dev packages, configuring VS to know where to look for those headers/libs, etc) so that I could more easily get instant feedback as to whether my source changes fixed the compile errors.
After a few hours of #include fixage and slight reworkings of some unix-specific code, we had a successful build of GMime.dll, woohoo!