In versions aired/distributed in most of the countries, castaways mention they have been on the island for a month, but Sawyer's hair has grown about four to five inches and is now so long that he is pulling it back into a ponytail. In the flashback that shows them boarding the flight in Sydney, his long hair makes him look noticeably different than he did in the pilot episodes.
Michael fires the flare and we see it fizzle out. However, in a subsequent shot, the flare is still ablaze.
When Hurley is running through the airport, he has two suitcases. Eventually, he doesn't have the blue suitcase anymore, and only carries one when he proceeds to enter the plane.
Charlie's forehead is bleeding and Sayid tells him to remove the towel. In the next shot the blood is almost clear and then, when Sayid is placing gunpowder on his wound, the blood is back.
During the flashback sequences for both the pilot and the finale, different characters are meant to be traveling through different sections of the plane, although it appears that, with the exception of business class, the same section was used for filming but with different people. This becomes a problem when spoken lines referring to seat numbers as well as the footage from right before the crash doesn't match at all to the boarding footage in the finale.
The radar that is attached to the raft shows a 360-degree view, but passenger airplanes only have forward-looking (max. 170 degrees) weather radar. This type of radar also typically runs from 115V, 3-phase, 400Hz current and cannot be connected to a battery directly.
The radar screen on the raft shows a rotating trace on a circular screen. To get this kind of display, the radar antenna must be mechanically rotated. The antenna on the raft is fixed in one position (pointing to the aft).
When Jack and Locke pull the hatch off the hole, the metal surrounding the hatch should have been bent, but it wasn't. With an explosion that large, the metal should have dents in it, but it was smooth like nothing had happened.
In a lot of shots with Aaron after Danielle has taken him, it is clear that the baby is fake. The most revealing shot is when Charlie brings him to Claire. Before that, as someone is walking towards the camera with the baby, you can clearly see the entire head of the doll.
In the flashback to Hurley trying to catch Flight 815 at the Sydney Airport, the name "Kamehameha" can be seen on a sign above a door. The sign referred to the Kamehameha Exhibit Hall at the Hawaii Convention Center, which doubled for the Sydney Airport during Lost (2004).