I've noticed very strange thing about Qt Creator on russian version of Windows recently.
The matter is that Creator by default offers to create new project in "My Documents" folder which in russian version (for example) is translated and using cyrillic symbols in its name. But after creating you cann't compile project due to qmake's error. I think this could be a little bit confusing for a new Qt users who just want to try Qt Creator.
Then I've found out that the problem is in way qmake recieves an arguments from system. It just converts them like this:
QString arg = argv[x];
So by doing this qmake disregards any locally encoded path names.
I think it could easely be fixed by using QTextCodec but I also have found defines like QT_NO_TEXTCODEC so I don't know whether it should be touched or no.
But anyway I think this problem should be tackled somehow.
P.S. And yes, there is no such a problem under Linux.