No implementation due to poor documentation
I have tried opening a OGG container with FLAC content in many players on Linux, Mac OS, and WinAmp on Windows. There is almost no support what so ever for this file type. Most players fail to recognize metadata (NEED STANDARD!!) in the FLAC codec, and some fail to playback the file all together.
Tried most recent version of Amarok, Banshee, VLC, MPlayer, Xine, iTunes + XiphQT, WinAmp...
I think this is due to poor documentation on the Xiph website. FLAC's site does OK, but I do think it should be made more promontant in the OGG spesifications how FLAC, Vorbis, and other codecs works. Should be mentioned in the Vorbis documentation that OGG is a container format, and can contain other formats as well.