.ogv files aren't recognized by the file open dialog
In VLC, go to Media > Open File..., and choose a folder that contains a .ogv video file. VLC won't see it, because this extension isn't in the "Media Files" or "Video Files" lists. We must change the filter to "All Files" to see the .ogv video.
Nevertheless, the .ogv extension is recommended in the Theora Specification for the MIME type video/ogg. See p. 139 of:
http://theora.org/doc/Theora_I_spec.pdf
An example of utilisation: the DVD ripper Thoggen encodes in video/ogg and creates files with .ogv extension.