It seems that this second half-life must be the difference for people who have more trouble sleeping long after caffeine intake. I wonder if this implies that their bodies have different maximum attainable amounts for the proper enzyme. I'm curious if anyone knows more detail about how the interplay between enzymatic saturation and genetics / gene expression works here.
Further, Pollan's interview suggested that even if I could sleep, caffeine was interfering with "deep wave sleep" - so I gave it a shot. I consider myself lucky that none of the headaches or [extra] irritability kicked in, so there's that.
So, while you might sleep all night. It's low quality sleep.
I think the awake/alert factor I get from having my morning coffee at this point is a learned response, not a chemical one; a decaf coffee is just as good at perking me up in the morning as a non-decaf. If it weren't for the headache spikes hurled straight through my brain by satan himself I wouldn't even bother.
Edit: That's not true, I actually do love the taste and ritual of making coffee too; it's a whole thing to me. It's like a Japanese tea ceremony, but with coffee.
But sometimes, when no one is looking? I make a third cup.