Oh god, that game had the worst blood effects EVER.
SPOILER:
Seriously, when Duncan stabs that 1 guy during the Warden initiation, just 1 little stab and his whole body from his hair down to his boots gets drenched in blood..
My problem with that is that it seems like the game just drenches your entire character in blood, rather than just adding a blood decal on the parts actually sprayed by the blood, which is how it should be. But in the trailer, the blood only covers the parts of the player that actually get sprayed by it, so it shouldn't be a problem in Skyrim. And yes, I think we can assume that the blood splatter seen in the trailer is indeed in the game, what is still up for debate is how much we'll get in terms of other instances of blood and gore, like whether we'll see dismemberment or visible wounds.
I hope the blood doesn't just fade into your sword like in Oblivion...though admittedly it looks and kind've cool and is fitting with Dawnfang/Duskfang
It has to fade at some point, aside from the performance reasons, if your weapon gets covered in blood and it doesn't fade, eventually it would be entirly drenched in blood, which you'd probably want to clean off even in real life, but unless Bethesda is going to add an animation for cleaning blood off your sword, having it fade away at some point is probably the best compromise. I just hope the decals don't fade as quickly as in Oblivion, I don't want to see them dissappearing right before my eyes before the fight is even over.