Hiya all. I'm already fortunate enough to have the game (released earlier in Europe), so I can provide some details on your questions.
The combat looks absolutely fantastic in the demo, but I am a bit alarmed by the "right timing" thing.
The timing is not very hard. The first fight you don't understand what the hell is going on (at least I had it). I tried to click very fast but that doesn't seem to work well (it doesn't). What you actually have to do is click once, be patient, wait for the cursor to 'light' up and click again. It's possible however that in the meantime you can get hit or your attack is parried, etc, making it impossible to continue the chain, so you just have to start over again. It's very important to be patient with your clicking. If you click too much you'll do very bad in combat. You have about 1-2 seconds to proceed to the next step in the chain, but you can't really miss it as all you'll basically do in combat is wait for the cursor to light up and click (and use some signs and maybe change your combat style).
Besides, all these swordfighting styles and combos... (Like who really used all those "lightsaber forms" in KOTOR?
You'll definately use the different styles! Some mobs almost seem immune to one style while they go down in seconds to another. There's a HUGE difference. This makes it a bit more interesting on first encounters with a certain type of enemy, but you figure it out pretty quick.
What I thought to be a bit weird though is that with the "Strong" style you really notice it works (very well) on one type of enemy and not at all on another. I kind of expected it to be the same for the "Fast" style, but I noticed that the "Group" style seems to do well against the enemies vulnerable to the "Fast" style. And more, the "Group" style seems to be better than the fast style! But, this may all yet change I suppose when I get more talents.
I hope I should be able to pause while in combat, to consult the manual
Yep you can. You probably don't need to consult the manual though. Your journal contains a lot of information too, also a bestiary with descriptions about the monsters and hints on how to deal with them. A bit like the journal from planescape torment, but a (much) more extended version.
Combat sounds really complicated
It really isn't. Left click to attack, right click to cast your active sign (spell). The only thing you can do wrong is click too early or too late, but that still wont kill you (medium difficulty is already rather easy, I'd pick hard if I where to restart). It'll just slow things down.
Has anyone heard much about the AI or seen interesting combat battles?
You are right what you saw on that movie. You are quite often surrounded by enemies, but I never really got the feeling that the enemies behind me where attacking at all. However, this may also be due to the combat style. When you use the "group" style you also do damage behind you. When mobs take damage they seem to have to 'recover' before they try to attack again. So often you'll just chain attacks at a mob without him even trying to hit you once (unless you get a parry or something). I am guessing this is basically what is happening when you are being surrounded too.
I had another encounter with 3 ranged mobs and they where tearing me apart, so that kind of proofs that they do in fact all attack.