On several Windows 7 and Windows 8 installations and for any printer driver we tried QPrinterInfo::location() always returns an empty string. This can be observed in the print dialog of any Qt application.
Included screenshots of the Qt Print dialog where the location is empty when it should be "USB001", as a native print dialog shows (in this case from Visual Studio, but most applications show that)
Oddly, in Internet Explorer 8, which uses the new print dialog, the location is also empty, so it's possibly a bug in Windows' new print dialog. But maybe Qt could inquire the printer location in a different way?