Oh, and there's a hidden 4th soul shard too, for future affliction bonuses.
Doesn't seem to be anything graphical for demonic fury. Guessing they just get more demonically pissed off.
The 4th soul shard is from a glyph, and soul shards is only used for Affliction it seems. But when you request soul shard numbers from the API with another talent spec it will act like you always have 3 (or 4 with the glyph) soul shards even though you can't use them. The same goes for demonic fury where there seem to be a base of 200 and when doing damage it will count towards 1000, even when you aren't speced into Demonology.
Demonic Fury is displayed in a bar with Demonology :)
I'm currently preparing my addon for MoP.
I've started with the Warlock class where I've found out by experimenting that:
UnitPower('player', 15) = Demonic Fury
UnitPower('player', 7) = Soul Shards
UnitPower('player', 14) = Burning Embers*
*But the burning embers only seem to go from 1 to 3 (integer numbers), even though I can see on the default blizzard GUI that I get a smaller amount of Burning embers when doing damage with for example 'Fel Flame', and it takes like 10 'Fel Flame's to get 1 burning embers...
So is there any 'top-secret' (easy) way of getting the 'real' amount of Burning Embers?
... And is there a place where one can read in detail about that kind of changes..? (wowpedia doesn't seem to provide much detail about this kind of stuff...)