Yes, and at least for me, good fantasy should have roots in reality. That's what ultimately makes the Potter books so fascinating for many kids and adults alike; they can relate to it. Rita Skeeter is one of the brilliantly nasty characters. She's out to destroy Harry's reputation with her now famous self writing poison quill.
But I agree, 'Sherlock´' should not drift into fantasy. That's wy I hope, MoGiss come up with at last a marginally believable solution for the Reichenbach conundrum. I remember, when I was watching the first Downey/Holmes movie, I was very annoyed, when it seemed to drift into supernatural realm. Eventually, the solution was not found there, but the whole thing was still too over the top for my taste.

I think, they play a game of mental chess with each other, just as kazza has described it. In the end M realizes, he is cornered and probably beaten. But I think, we don't see all the chess pieces, yet. Sherlock has realized, that there IS a recall code, and if he applies pressure at the right points, M might call the snipers off. M says first, that nothing could make him do that, but SOMETHING, we are not aware of yet, seems to change his mind. He kills himself to make it absolutely impossible for S to get the recall code out of him. He even says so: 'As long as I'm alive, you can save your friends, you've got a way out - well good luck with that'. Then he shoots himself and thus forces Sherlock to go through with the jump.Since he believes, S will also die, M might consider his suicide a draw in this match of mind chess.
I think, M's actions are completely logical, there are just a few missing pieces. I feel, a formidable adversary like M does not kill himself just because S looks sternly at him and tells him, he's not an angel. Also, a supersleuth like S doesn't confront his psychopath arch enemy with nothing in his sleeve than his talk and his stern look, though I have to say, that he does manage to look at M  like Lucifer himself before his fall.

sioneld, I've seen the sequence of grabs. Thanks for linking. All, I can say, is that I agree with most of the remarks, except one. In the last picture of that sequence, I can make out definitely the object I'm talking about all the time, only it is rather blurry and looks more like a reflection of light, while it appears much sharper on my screen. And a split second after that grab it can be seen even better. It's moving and turning a bit in S's hand. It's definitely a tiny hook. You have to take my word, that I'm  not under the influence of the Baskerville psychedelic fog,lol! Anyway, I can only prove it, if I can come up myself with a decent freeze. If I make any headway I'll let you all know. The significance of that is another thing altogether. I've come across another blog, where someone has also made out something in S's hand, and has quite a few intelligent thoughts about it. I'll will adress this later, since real life makes some urgent demands.   
kazza, thank you for the pictures!

Yes, Irene, I always believed, they are not just trash talking each other... something VERY specific is going on there...
Do you ever have the feeling, that we could use our collective energy for solving more important problems, lol? But I just don't like unsolved riddles... maybe that's one thing, we all have in common.

Is anyone following Preston/Child's Agent Pendergast novels? This character, with his freak physiognomy and emotionally detached intellect owes a lot to Sherlock Holmes - now, that I think of it, it might not even be coincedence, that his brother is named Diogenes and had equally stunning intelligence, though he was definitely NOT on the side of the angels. He was the arch villain. He's supposed to be dead -  but nobody is QUITE certain...
Anyway, the last novel finished with an impossible cliffhanger as well.
For awhile the web has been abuzz, who should be casted as Aloysious Pendergast, should they ever make a movie, which is not certain, since there seem to be legal problems. There were many suggestions, Paul Bettany being one of them, but since Sherlock, Ben Cumberbatch's name is coming up more often - he would make a stunning Agent Pendergast. I couldn't think of anyone better suited for the role. Only problem: Pendergast is from Lousianna... so there could be a problem with accents.
The books themselves are like pop corn - lightweight, but once you started, you can't stop eating, lol!

Ok, I will describe the object, I see, a little more detailed: The metallic hook looks like one item of those little multi tool swiss knifes, like the one M left sticking in the 'poisoned' apple in S's appartment. I'm not going to interpret this. I'm just stating what I clearly see.

Irene, I noticed the same things. This exchange between M and S is most fascinating - and Sherlock has definitely something in his hands, when he is about to make hand contact with M (the handshake). I can see it very clearly, when I run my dvd in super slo-mo. It's black and metallic . The metallic end has a small hook, which is protruding from his fingers just a tiny bit. It has the size of a key. When M closed hands with S he must feel it.
I don't think, Sherlock is a junkie, though he seems to have issues with drugs on and off, when he is bored and unchallenged. In SiB John and Mrs. H search his rooms in 'all the usual places' for drugs, and S picks up on it immediately; so it is probably not the first time they are doing this. Also the hilarious drugs bust in SiP alludes to a drug history Lestrade is aware of. I belong to the  school of thoughts, which believes in the Rhododendron Ponticom clue, though I'm not entirely sure, what effect he wants to create by taking it. It slows down the cardiac rate and makes for watery eyes and a runny nose, but it certainly doesn't make the pulse disappear. And I think, IF S takes some drug, it's right after M shot himself.
When you run the lab scene in slo-mo, you can see, that S pockets the rubber ball, before he goes to his roof rendezvous with M.

kazza, you should give at least the second part of 'The Hobbit' a try. To cast Ben Cumberbatch as Smaug vs Freeman's Bilbo was a stroke of genius. The dialog between Smaug and Bilbo could be wickedly funny, if they stick closely to Tolkien's book. The whole book is full of brilliant satire, something, we do not associate with LotR. I wonder, when the casting actually happened. Was 'Sherlock' on the horizon already?
Irene, yes, always the wait... But nothing was worse for my sons and me, than the years of waiting for the final Harry Potter books. They grew up during that time. But by the time the last book was published, we had figured out the central mystery (is Prof. Snape good or bad, and why did Dumbledore trust him) pretty correctly with the help of the world wide web.
Did the article say, Sherlock 3 will be aired in the LATTER half of 2013??? Damnit!! But, I'm sure, by then SOMEONE will have figured out everything. Problem: We won't know, who figured it out correctly!

I've dropped my phone so many times, that I encased in kind of a shock proof rubber envelope. Now I could safely jump from a roof top with it.
AC Doyle wrote a lot of false things, too. One of his most famous stories- 'The Speckled Band' - is based on a creature (the murder weapon), which totally doesn't exist:  An Indian snake he calls 'Swamp Adder', which is trained to climb up and down on a loose rope, comes back, when you whistle, and drinks milk from a saucer. Sounds more like a kitten to me, lol!

How could Molly know about dead M? I thought about that a lot, too. If my second theory, that the whole thing will go down as Rich Brook's suicide, is correct, this is not a problem. She doesn't have to know.
Otherwise there is the possibility, that S phoned Molly and told her to remove M's body (which won't be possible without Molly having some help, of course, since M was not fat but a grown up man), and tv just did not show this phone call. For me, that's the least likely scenario. Also I cannot imagine, that Molly would  arrange a cover up on her own accord, since she was probably ALREADY assisting Sherlock to go underground, so there was no need to protect him from any kind of short term consequences.
Or S had always planned for M to be dead, suicide or otherwise, and had made arrangements with Molly (and other helpers) beforehand, what to do with the body. The possibility, that Sherlock had always planned M to be dead, is appealing, because in the original story Holmes is more actively involved in Moriarty's death and triggers his fall by applying some kind of martial arts movements, called 'baritsu' by Doyle. It would also fit in neatly with his talk about not being his brother(who let M go after the interrogation), being on the side of the angels, but not being one of them, and being ready to shake hands with M in hell. Also, since S planned his own fake death in advance, he must have had some plan, how to prevent M from discovering the fake(if the fake was visible from the edge of the roof top, that is). If he planned him to be dead, this would not be a problem. The big question here is, how he planned him to die, because triggering a suicide is a VERY unpredictable procedure - unless you have a REAL good instrument for applying pressure, like the cabbie from SiP, or like M himself, who turned S's friends into hostages. Also S seemed to be genuinely shocked by M's sudden suicide.