[Pazuzu]

Ethan in LA makes perfect sense.

Let's go through the "alternative" timeline.
1977, the bomb goes off, triggers the massive electromagnetic anomaly, and the Island is destroyed (we see it on the bottom of the ocean, it's gone). Everyone currently on the Island dies.
The women and children were transported OFF the Island before this happened. that would include Ethan, Charlotte, Miles. Ethan took the name Godspeed because his mom was with Horace before they left, after his (Ethan's) father was killed.
Eloise Hawking, Charles Whitmore, Ben all all dead (drowned). It's safe to presume that Richard Alpert, the Others, and possibly Jacob/Nemesis are dead, unless they have some particularly powerful supernatural abilities.
Daniel Faraday is not born (Eloise was pregnant at the time of the Incident).
Penny Whitmore is never born , since Charles is dead.

Desmond Hume never goes to the Island, since he cannot enter the race run by Whitmore, and wouldn't anyways (no Penny).
The freighter team never travels to the Island.
The French scientists presumably die in the ocean instead of being stranded on the Island. The transmitter is gone, so no numbers being sent, and no French message.
Hurley is lucky because he's never encountered the numbers, but he still won the lottery.

Jack and Desmond never meet (at least the way they did at the stadium), since Desmond isn't training for the race.

Now, why is Hurley on the plane? His reason to be in Australia was directly caused by the numbers. Is it the same "timeline" need that let him win the lottery, and so he decided to go out there for the heck of it?

Now, there's another problem. Despite all of the "troublemakers" being dead (Charles, Eloise, Daniel, people who caused various interactions and been on and off the Island), it's safe to presume that the entire world knows about the Island. Not only was there an atomic blast in the ocean, but boatloads of women and children arrived somewhere, saying "we left our husbands on this Island, we were doing research that no one knows about, go save them!" Eventually, knowledge of the Dharma group (and likely Hanso and DeGroot and the Ann Arbor connection) would be well known. Someone somewhere would eventually go hunting for the Island, and find it on the ocean floor.

So, what have I missed?

The only error that I've found so far is that (it's presumed) that John Locke died, or was going to die, when he went out the window. Jacob touched him, and seemed to bring him back. However, Jacob should be dead at that point, so why is John alive to be on Flight 815? Also, he wouldn't have encountered Kate as a child, and therefore wouldn't have bought her the lunchbox that played so closely into her back story. He would have encountered Sawyer, since that happened in 1976 when he wrote his letter.