I am a big fan of this series and have a couple of theories of what I think is happening and wondered what others thought, just wanting some insight.
I think the people got on the plane and never actually crashed. I think they were gassed and taken to a government (possible alien) location and their minds were feed the reality they think they are experiencing. Because they are in this state, they learn that by thinking things, they can create their own reality. For example, the young boy would read about items in a comic book and they would appear (Polar Bear). The woman thought of a horse in her past, and it appeared. The doctor thought of his dead father, and he appeared. The Priest/Drug Smuggler, thought of his brother and his brothers plane was found on the island. In any case, they seem to have a dream like control of their environment and the longer they are there, the more it seems to mold to their own reality. I think the "others" is actually just a small group, but have learned to create their reality when they want and that is why their fellow others seem to appear out of no where. The reason the others took some of the people, and not others, is that some of the people were not taking to the drug correctly and had to be removed from the reality. The reason the children are taken, is their imagination is stronger and without control, could cause serious problems. I think in time the series will start to show that the castaways are actually making things happen more and more, that can not be explained by nature or others. I think in time, the others will be revealed to be military personal that were used first as an experiment and then could not escape and have been their for decades. I also think, in a short time the dead ones might start coming back for no explained reason, other then they just reappeared. Oh, and the voices in the jungle are the scientist speaking over the bodies in the unconscious state, being heard by the others in their dream state.
Okay, next ... looking for theories