I was crewing around texel in 1998, out on the wire eating a mars bar when the hook sheared away from the plate on my harness. Luckily I managed to keep hold of the jib sheets and so was not completely seperated from the boat, we soon got back up and running again after swapping harnesses.

With most mishaps you get some sort of warning (even a pitchpoll happens relatively slowly) but with this one I went from happily sailing along to being in the water in a split second.

I've never considered tethering isn't this just one more thing to get caught around the rigging if the boat turns turtle?