Back in the early nineties, I used to be fairly casual about the seat belts---till the day the oil tanker was wrecked on Shetland shores ["Braer"?]. That just happened to be the day I was flying Prestwick to Toronto en route to Vancouver. For some reason, the flight path leads almost due north for the first part of the journey [still does, in most cases], and when we approached the Shetland area things got more than a wee bit rough! That was my most telling lesson regarding the benefit of seat-belts, I can assure you! [ Captain's comment on intercom--"She doesn't do this very often!"] Not as vicious as hitting the jetstream of another plane though-----