If you haven't seen season 2 of the BBC's Sherlock, don't read this. Unless you like spoilers.
*spoilers*
*spoilers*
*spoilers*
Okay, this is my theory of how Sherlock survived the fall from the building in The Reichenbach Fall:
He never jumped.
We see John get out of the taxi, and Sherlock directs him to stand in a certain place and look up and says he's on the roof. So when John looks up, he would assume the figure on the roof is the one he's talking to on the phone.
Sherlock also tells John specifically to keep his eyes on him. Which means there is something elsewhere that John cannot see for the trick to work.
I'm guessing Sherlock is on the roof of a building nearby, perhaps behind John. That is where the confrontation with Moriarty took place.
The other rooftop is where Sherlock arranged with Molly - when he asked her for help earlier - to have Molly standing with a body from the morgue of Sherlock's approximate height and weight (it wouldn't have to be perfect, the angle from ground to rooftop would skew perspective) and dressed in Sherlock's clothing.
On Sherlock's signal (he could do an arm wave, since John can't see him), Molly would drop/push the body off the ledge and splat.
Then that bike-rider (part of Sherlock's network) knocks into John as he runs to the corpse, not only delaying him so a crowd has gathered and he can't actually touch the corpse, but the rider has injected him with project H.O.U.N.D stuff (borrowed from Mycroft? since he owes Sherlock) so John is bleary and disoriented when he gets to his feet. And then sees precisely what he expects to see, what he most fears when he catches a glimpse of the corpse.
And then Molly can do the paperwork to say it's Sherlock in the morgue now, sign him officially dead.
That's how I think Moffat & Gatiss did it.
