Simple question:
All-Out Attack / Guarded Attack combine with Swift Attack? Can someone use All-Out Attack, and gain +20 to WS for... 3 attacks (Ordinary + Swift + Lightning)?
All-Out Attack / Guarded Attack combine with Swift Attack?
If I understand the rules correctly, then absolutely not. Each of those actions (All-Out, Swift, and Lightning Attack) is its own unique Full-Round Action. They cannot be combined, unless the rule for the specific action in question specifically says so. I don't believe that any of those do ... at least I hope they don't.
It also sounds like you might want to download the official Errata from the DH Support site. It clarifies these and other rules.
Hope that helps. 
I've checked errata, but found nothing there, regarding the topic :-(
No, as Sister Cat says the All-Out Attack and Multiple Attacks actions are distinct Full Actions. With only one Full Action available in a given round you can only perform one of these actions to either perform one Melee attack at +20 WS or 2/3 attacks with the Multiple Attacks Action (but not both).
Although furious attack MUST be combined with All out attack. Which is a fairly good chance of an additional attack at later levels.
Face Eater said:
Although furious attack MUST be combined with All out attack. Which is a fairly good chance of an additional attack at later levels.
Quite right. But as I said, the rule for the Furious Assault Talent 'specifically' says how you get the extra attack, by spending your reaction for the round, and since it must be used with All-Out Attack, it still can not be used with Swift of Lightning Attack. 
Furious is a good way to get extra attacks in if you really need the 20% bonus. It's less directly controlled as you do need a reaction event to come up, but you still get the attack bonus. As with most things, it's a game of compromises.
Filadan said:
Furious is a good way to get extra attacks in if you really need the 20% bonus
Or if you're frenzied. It is, in fact, the only way to get multiple attacks while frenzied.
Furious Assault is also great if you want to use Frenzy for the rather nice bonuses and immunities, but want to attack more than once per round and have something to do with your Reaction.
Firstly, I agree with Sister Cat's post:
"If I understand the rules correctly, then absolutely not. Each of those actions (All-Out, Swift, and Lightning Attack) is its own unique Full-Round Action."
completely. What exactly the 'correct' rules for Frenzy are - I'm not sure, since I can't believe designers would have made it so that frenzy and swift attack cancel eachother. But a correct reading of the rules again says that all-out-attack is a full action, so is swift attack, so you can't take them both.
HOWEVER: In all my games I completely ignore this. Why? Because the 'correct' rules make melee combat much less interesting. Having frenzy + lightning attack + other nasty stuff *should* make your character a grotesque combat monster, since A: the next guy with an autogun and manstoppers (or more likely by that level, plasma gun, two bolt pistols, or equivalent ranged horror) could still end them pretty quickly, and B: the WH40K universe is all about close combat being exceptionally brutal, swift, and decisive. So I let a character choose a fighting 'style' (normal, all-out, or defensive) regardless of what else they're doing - though of course Frenzy places a limit on their choices :-) Lightning attack + attack for two-weapon-wielder + defensive stance? Sure - they're leaping around makes lightning slashes while keeping their distance.