FWIW, my problem is the oft-asked "How do I call functions in a Windows DLL from an ELF process?" I appreciate WineLib is an option, and have run into a number of snarls along that path:
Well, see me discussing that with Bill a few days ago on the mailing list archives. Basically you have to make the whole ELF process into a WineLib app, at the moment you can't just call out from a standard linux binary into WineLib. IIRC mplayer does this by copy and pasting some wine code, then hacking it lots, even then that's only for codecs which are extremely simple programs.
The basic problem is that there isn't any good way to initialise WineLib without using the wine loader program at the moment.