On Sacrifice to Caiphon, I don't think I'd have as much of a problem with it if it were paragon tier - taking ~7 damage to retry your encounter power is a lot harder choice than taking 1 damage at 1st level. It's a weird feat in that the penalty for using it becomes more and more painful at higher levels.
But that aside, the fact remains that people other than warlocks miss with their encounter powers too, and they can't do squat about it (unless they have reroll powers). I definitely think it'd be a stretch to say that warlocks miss more often than other classes; depending on the enemies they sometimes hit significantly more often. I just don't like effectively giving all warlocks' encounter powers the Reliable keyword. The point isn't that you missed and wasted your turn already - that would be the case whether you were using an at-wil, encounter, or daily power. It's that you get to try again, and again, and again, and again, until you hit with that encounter power.
It is very thematic for a warlock, and I absolutely love the flavor, but I just don't think the tradeoff is good enough for the benefit. 1 HP to retry your 2nd most powerful power isn't really a "sacrifice" in my book. Perhaps if the penalty was higher? Not sure how to work that though.
About Two Fold Pact, I suppose that by the time you hit Paragon you're using your at-wills less anyway. Though I'm still wary of letting a human 'lock get all 4 warlock at-wills ...
For what it's worth, I have zero problem with the powers in this article bringing 'lock damage up a notch, I think they need it too. I was just wondering if that's what other people saw too.