This is the only place I can ask this question since the WineHQ forum is locked for some reason... So please tell me if I can statically link Winelib with a commercial application and what are the terms of its use - should it be acknowledged in documentation, application's about box, etc.?
A couple of points:
You can't really link with Winelib statically. I mean - you probably can, but it you still need almost all of Wine's infrastructure, anyway. Winelib is 95% of Wine, basically everything minus the PE-Loader (the code that can read Windows executables).
Wine is licensed LGPL. IANAL, but that means you can distribute Wine with your commercial app without being forced to open-source your own code. It works as follows: When you combine your app with Wine you create a derived work (or your app and of Wine). The GPL requires a derived work of free software to be free software as well, the LGPL does not. Still, if you modify Wine-code to make it work with your app, you need to make the modified Wine source available to the people you distribute your product to. The license lists several options on how to comply with the source code requirement.
You need to include a notice to the LGPL wherever your app provides its own licensing information. Read the LGPL for the details.