I've been told that the Mac will write files to the P2 card upon mounting in the Finder so I decided to find out. Here's what I did to test:
1. With the camera not connected to the Mac format a P2 card.
2. Shoot a test clip.
3. Turn off the camera.
4. Switch the Lock switch on the P2 card to PROTECT.
5. Turn on the camera and mount the P2 card on the Mac.
6. Fire up the Terminal and type in (with out quotes) "cd" hit space bar then drag the icon of the NO NAME P2 card to the Terminal and hit Return to Change Directory to the P2 card.
Your Terminal should read something like this: cd /Volumes/NO\ NAME
7. Type "ls -a" which lists all, including hidden files.
8. You should something like this:
Ok, cool, so with the Write Protect tab ON that's what's on the card from the camera untouched by the Mac.
Let's try it with the Write Protect tab set to OFF.
Just mount the card like you normally would but leave Write Protect off. Now, with the unlocked card mounted run the Terminal steps again. After "ls -a" you'll see:
So there you have it. The Finder WILL write to a mounted P2 card without you having to do anything. Has that caused a problem for me in the past for the thousands of cards I've loaded in in my life? No, but the possibility is there that the Panasonic camera may not like the files that are on the card after mounting.
My new rule of thumb is to lock the cards before mounting them in the Finder…just in case.