Re:OS X needs VLC (Score 3, Informative)

I couldn't get OS X to use VLC by default. Selecting "open with" VLC ALWAYS only works for that single file, not the file type, despite it saying so.

To set a default application for a file type in OS X, you do the following:-

Right click on any MKV file and choose 'Get Info'
In the 'Open With' section, choose VLC
Click the 'Change All...' button underneath.

All MKV files will now open by default in VLC