I just flew SFO-PEK and ICN-SFO in C, and must admit I broke the rule, since my MacBook Pro easily fit into the seat pocket w/o any protrusion. So I left it there for the duration, well except when I was working on it. I think the rule derives from the days of very bulky laptops, and agree that if this was still an issue, then during turbulence the FAs would ask us to all stow our laptops in the overheads or underneath the seat in front of us. Since they don't....well, let's just say I'm not a good role model. Let's not start on cell phones....