It's when one whizzes past your nose and you look at everyone else in the class because you know you got away with it.
I've experimented SO much with hand position on hooks, looked for definitive answers in boxing manuals, watching videos, etc and now generally put it down to personal preference. I've found landing palm down (as simon is doing in his vid) often torques my wrist. Throwing "palm in" stops that happening (but as you say falls apart as the hook gets longer). I can throw palm down (even when close) but I have to be much more aware of my hand and wrist placement in relation to the target surface so it's not as "natural" for me. Lukcily I've seen boxers landing with both types so again I think personal preference and context comes into it.
Get your coach to teach you to throw it with power at close range (so close your foreheads are touching),then longer range hooks will fall into place.
Thanks Knee Rider! Sylvie has tons of other good videos too but I also found this one in particular very interesting:
The left hook is just about the only punch I CAN do well in boxing. I agree that palm position seems a matter of preference. My coach always told me to go palm down but I always hit it with my palm facing me, for the same reason as Smitfire. As a guy with shorter arms than most my go to game plan is get up close underneath the arms and "climb the tree" with punches - the left hook is always the big one at the end. Coach is also great at hitting them defensively - he gets you jabbing in and times it so that you walk onto it (the lead hook).
When you're a southpaw and been watching this thread for weeks thinking, "Why they all talking about rear hand punches and posting videos of front hand punches?"