Originally Posted by mander
Track cyclists are always in the drops, except maybe when warming up or goofing around. They generally have their bars set higher than typical semi-clueless street riders.
Indeed. Drop stems come from an older fistful-of-seatpost fitting standard.
How much drop, drued? That depends on a person - on how long their various body parts are, their flexibility, and whatnot. Pro teams do a bunch of aerodynamic testing - the test various aerodynamic positions of a rider, and then they go out, set up a bike, and run a bunch of power tests to determine maximum aerodynamic advantage and maximum power output.
Some rules of thumb are, your elbows should be bent, you should consider riding longer, not lower, if you're trying to get into a decent race position, aim for a flat back, and don't be in a stiff-armed position.