In reply to planetmarshall:
Part of the 'appeal' of the Fig 8 bunny ears is that it is 'equalising' - that is that it is easy to pull rope from one loop to the other (as it is a fairly simple and short path around the back of the knot). It is this easy equalization that means it can fail if a loop is cut.
It is a totally safe knot if you don't cut a loop. If you are doing rigging/crag rescue etc there should be no way in which the rope should be cut, and so it is safe. In caving, where the rope will not rub with good rigging, I am more than happy for other people to do it and if someone asked me to do it I would. With certain rope types it may not slip anyway. If the knot is pre-tightened it may not slip anyway. If you pull one loop hard enough from a loose-ish knot I would be surprised if it didn't pull through eventually, but it might hold bodyweight or more (or less).
It is reliable partly because having a loop cut is normally just not a concern. It is not a redundant knot in the 'cut-any-one-strand' sense (but many/most of our knots are not).