Of course there is time travel, and it's not limited to the island.

[Cowboy Up]

it also might have to do when you give yourself to the island...or however Ben put it to Locke...you have to make a gesture...Lockes case killing his father...

[Ladybug]

maybe there's a really good plastic surgeon on the island.

[thebeann]

The finale also smelled like some timeshift thing. Like Jack referring to his dad like he was alive, then we come to find this is not a flashback but a flashforward after the rescue. Part of me thinks, well, maybe his dad IS dead and he's just crazy drunk. Just because no one actually said, "Um, Jack...I can't go "get" your dad to see who's drunker because he died back in 2004" but maybe they were just rolling their eyes because Jack always talks about his dead dad as if he were alive when he's stinking schnockered.

On the other hand...if we take at face value (and at some point, you just have to believe what you see and hear on the television), then it makes sense that something changed. Yeah, I know...very "Back to the Future II" but there is that philosophy that if you could go back and change even one thing, the cascading effect could be enormous. Jack's dad didn't die, Kate didn't leave her cop husband (if in face he is the "Him" she talks about in the finale)...the butterfly effect.

Unfortunately, that philosophy doesn't entirly support the Desmond effect, which is "no matter what I do, you're gonna die, Charlie." NO matter what I change, the universe will set it straight.

I can't think about it any more. My head hurts.

[therealsawyer]

I don't think Des' "course corrections" always just happen. 

If so why did the "clock lady" seem to get so concerned and try to talk him out of proposing to Penny?

I think you can change the future but she and those that she works for didn't want Des to not end up on the island.  I think at some point we will find out what happend to Des between when he was hit by the Cricket bat and when he ended up back on the island buck naked.  Something he doesn't even know about because he has to believe in fate so that their plan will remain in place, including Charlie's death.

[DirtyMaggieMae]

That's a pretty good point beann.  Ok, i've only been to local small town pharmacies, but all the pharmacists know the doctors, so i think they'd know if one died three years ago.  Ah well.  She couldda been new.

[Cowboy Up]

She could have known and tried not to be mean...knowing Jack was out of it...