Graphics card that can't handle working to its full potential is already dead (as designed).
It was not required for my app to know about network adapters. Is that possible to do in cross-platform way using Qt -- I have no idea.
I concur. My Qt-powered multithreaded and networked (TCP&UDP) application is compiling and working nicely in linux, osx and win32 without any os-specifc #ifdefs.