It didn't seem to me that Desmond had any kind of clarity at all on the island. I mean Widmore never even explains what he wants Desmond to do, and Des just agrees to help him. Then Sayid kung fu's his way out of the jungle and tells Desmond that these people are dangerous, and he needs to go with him, and Des just says yeah. He seems very zombie to me. At least ON the island anyway.
I don't know if he is so much a zombie as he is just going along with his fate. He's been through this dance before, trying to save Charlie etc. He may just believe that resisiting his path is pointless and the universe will course correct anyways, so he's just going with the flow to get back with Penny.
sort of what I'm saying. you're saying that anyone who comes along and tells Desmond to go with them he'll go because it's his fate/destiny and he doesn't want to fight it. I'm saying that he will go with whoever because he doesn't know any better at the moment.
OK, I think I understand. But when you say, "he doesn't know any better" do you mean he is kind of lobotomized (for lack of a better word)? Like if someone said, "He Des, wanna get punched in the face?" He'd reply, "Dah, OK." Or do you mean it more like he has no idea what his path is, just that he needs to walk it?
I think he would reply with, "Um, why?" then when he got his answer, he'd say okay. At least that's the way it seemed to me.
Does anyone have any thoughts as to what he plans on doing with the Oceanic Flight 815 Manifesto? Bring them together, he just wanted names? For what? How?

He needs the names of the passengers because they are all (mostly) strangers. He has no idea who these people are yet and he needs to show them that they have a different destiny than the life they think they know.
I think that the "something" he wants to show them, is the other time line. Daniel told Desmond that he had his feeling when he saw Charlotte from across the room, so maybe he's hoping that getting these people together will have some sort of stronger affect on all of them.