I agree that Desmond seemed kinda zombie-ish. ..
I'm going to strongly disagree with all the zombie, accepting fate theories
I've been thinking that he seems like he knows what he has to do and is determined to do it... If he succeeds he'll have both the love of Penny and the respect and love of his father-in-law. However surprising it was to us and Widmore's goons that Sayid jumped out of the jungle, Desmond knows that was supposed to happen and how this is where he has to go to achieve his end game.
I much more agree with this ^ ^
Desmond is absolutely aware that there is 2 timelines.
He is aware of this on the island and he is aware of this in the alt timeline.
He is aware that in one he has Penny, and in the other he doesn't (well, he just met her)
He is aware of this on the island and he is aware of this in the alt timeline.
He knows that Daniel has created this alt timeline.
He is aware of this on the island and he is aware of this in the alt timeline.
He knows he has a purpose and that purpose is him and Penny
but I'm not so sure about the "Desmond knows that was supposed to happen"
maybe, maybe not
I thought his smile was similar to Charlie's lack of response when the car crashed into the water. Charlie didn't panic. He just sat there and accepted it because he knew that "life" wasn't real and didn't matter. His real life was with the unknown blonde.
In the same way Desmond's smile was a smile of laughter. He's laughing at Sayid. He's laughing at fate. Des is thinking, "you can't hurt me. you can't stop me. I will be with Penny in one life or the next. Whatever you do to me doesn't matter. I laugh at your feeble attempts to scare, imtimidate and stop me."
Des is a man with nothing to lose. He laughs at fate.