I am having a couple of issues with my "Data" external HD volume that I've setup as a poor-man's NAS (attached via USB to my AirPort Extreme).. Lately I have been experimenting with the various media players for OS X and seeing which one works best for me (VLC, Perian + QT, and Plex). So I selected a random *.m2ts file (from a BD-rip) and then "Cmd + I" to "Get Info" for that movie. In the "Open With" drop-down menu I selected "Plex" (as Plex seems to do a better job streaming than VLC for this one particular mpeg stream file), and when I tried to change it to Plex, it reported that I could not change all files to open with such a program (which is what I was used to being able to do). See screenshots for some visual cues.