In fact I wouldn't have thought of it but for a normal desktop file transfer that was going to take an inordinate amount of time... Something like over an hour...

Fact was though, I had just copied a bigger file to the Firewire disk and it had been zippy: under 5 minutes.

So what had happened in the meantime? Simple, the single memorable (?) thing i had done was that I had plugged the iSight...

So, on a hunch, I stopped the suspiciously slow copy, unplugged the iSight and reinitiated the copy: low and behold, the copy to the firewire disk proceeded briskly and completed under 3 minutes instead of the projected 90 minutes...

Simply plugging back the iSight, I can reproduce the situation at will,