+1, I've had my car up by the diff 50+ times probably. My jacks all have the little rubber pads on them though. The diff is a pretty gnarly piece of metal, I wouldn't worry about it.I never used anything between the jack and diff, too concerned with the car slipping off. No damage done to the diff after 3 years.
I was waiting for someone to say itLotion is a good way to jack, just make sure you have tissues or a sock close by.