Not only do I keep my seatbelt securely fastened during all aspects of flight (aside from the very occasional relief trip) I also keep my hands securely fastened around the seat arms. This, in turn, creates that white-knuckled effect. Said white-knuckled effect lasts for the duration of any given flight. Can you say: fear of flying?!!!!!!
(Said death grip on seat arms and seatbelt tightened to the point of semi-suffocation is usually, however, mitigated by copious amounts of alcoholic beverages. Preferably served free of cost.)