At least once a season, there comes a point where the writers of Lost seem to go on their own vacation and try and fill time until the countdown till the final season begins. 'Dave' would seem to be one of those episodes, but there are a couple of points that may prove valid to the series as a whole, as well as a couple of loose ends that the writers of the series are never going to wrap up.
The episode is centered around at what was one of the early theories of what the island is--- that it was a hallucination of one of the characters. We know now that Hurley spent some time in a metal institution, and he is probably the most popular guy on the island. Are the [people an extension of his personality? Or is there another reason that he hasn't lost any weight on this island? We've known that he has been holding on to a stash of food, and when he finally confesses his sin to Libby (we'll get to her in a minute), her reaction is not one of someone who's been eating mangoes and fish for two months. Rather she encourages him to destroy it, This leads to the appearance of someone who makes Hurley very nervous.
The person he sees is Dave, obviously, and he was one of the people who he knew from Santa ROsa. We learn that he was nearly catatonic after an incident where he stepped on an overcrowded, causing it to collapse and two people to die. He has blamed himself and that is why he hasn't changed. Dave was a manifestation of his personality--- the part that didn't want him to get better. When he realized this, he managed a breakthrough, and things got better--- for a while.
Now Dave is back, and his telling him this same hallucination theory. He adds the fact that the numbers are still recurring everywhere, we've been seeing them around a lot, including with the Dharma Initiative, and now he convinces Hurley that this is cycle that he has to break. Hurley then tries to find a way to break this theory.
Here's a more pertinent question, because it's never been asked, if Dave is hallucination, why is Hurley seeing him now after all this time? Does he think that his eating is putting people at risk somehow? More interestingly, what if Dave is one of the first indication that the island is 'talking' to him? In later seasons, Hurley will show evidence of being able to tap into a vital force of the island (I won't go into details) and even when he is off the island, he will continue to see people who can't reasonably be there. Is it possible that Hurley, like Locke and Eko has some kind of communion with the island, and that it is trying to test him? Perhaps the island feels that Locke is not quite passing the trials, given his attitude of the past few weeks, and maybe it senses Hurley--- the only person who is certain they're on the island In the end, Libby convinces Hurley that this is a real by saying that she knows something that he doesn't. However, we then get the final twist--- that Libby was also at Santa Rosa. At the time I thought that this meant that this was some kind of hallucination, and Libby was another part of it. Then, of course, there's the point everyone made--- if Libby was really there, how come Hurley, who clearly remembered a lot of other patients, didn't remember? Was Libby some kind of doctor. We find out later that she has connections to a couple of other people on the island--- is it possible that she's an Other? There are definitely possibilities, but the writers never tried to explain or explore them.
Far more interesting things are happening back in the hatch, with the re-interrogations of the Other formerly known as Henry. What's never been quite clear is how not-Henry got caught in Rousseau's. Everything this man has done is by design, so why did he come to this side of the island for? Why are the Others, who up until now have made covert attempts to move through the Others, and who threatened the Losties with violence should they try and find them deliberately infiltrate them? Not-Henry says he was following orders (even now there's a possibility that he's telling the truth), but why come like this? And, despite what we says, he knows very well what happens if you don't input the numbers into the computer, so why is he lying? If he is trying to protect the island, why would he do something that he knows very well could lead to massive casualties? We're still waiting for answers on that one
Though 'Dave' does have some interesting moments and raises some interesting questions, for the most part, it feels a lot like 'Fire + Water,. We're running in circles, and even though interesting thigns are happening --- what was up with the food drop? what were Charlie and Eko building?--- we don't seem to be getting answers. Even if it does explode one of the major theories, they could've done that and done more in the hatch. So why keep us here anyway? It was nice to see Sawyer take a beating from the man he has antagonized the most--- but then, maybe that wasn't real either.