Here's a strange one: A friend of mine was editing some multicam footage and suddenly -apparently without reason- it started to severely choke his mac to the point where multicam footage would only play for about 2 seconds before giving up and announcing dropped frames. Literally two seconds.
I tried everything: rebooting, reconnecting his drives, repair disk, repair permissions, all the traditional troubleshooting steps. None worked. Then I tried a safe boot and it didn't take. The mac refused to boot into safe mode, so on a hunch I tried the firmware boot selector by holding down Option when the Mac booted and was prompted for an open firmware password.
So I turned off open firmware password by booting with an OS X install disc and then ran safe mode and zapped the Pram. The choking was gone. Multicam was working again.
So to determine if it was the open firmware password he set recently, I turned it back on and as I suspected multicam choked again.
Now, I'm not sure why but it's 100% consistent. No open firmware password and multicam works. Set an open firmware password and it chokes badly. He's using 4 separate firewire drives for his footage and media files so my only guess at this very strange problem is that somehow when the Mac boots having the firmware locked is preventing something between FCP and the Firewire bus or the drives.
I'm not sure. Any ideas?