I’ve been trying to figure out the Island, and I’d like to speculate that it’s a type of Tesseract.
http://en.wikipedia.org/wiki/Tesseract
You can express this shape in n-dimensions, and it looks different from each. As a 4-dimensional structure, a 3d visualization is only a slice of it. Likewise, to view a 3D structure from the perspective of a 2D universe only shows you intersections and masks the true nature of the shape.
Why am I going down this rabbit hole? Because we haven’t gotten a good explanation yet for a bunch of things:
[ul]
[li]The Numbers - Winning the lotto, being part of Kate’s safe deposit box number, being the flight number (815 is part of the sequence), the odometer, all the other places where it shows up.[/li][li]Polar Bears showing up both on the Island and in the pre-crash comic book[/li][li]Desmond’s description of the island in a snowglobe and the image of same in the pre-crash comic[/li][li]…and other off-island hijinks[/li][/ul]
How would this explain it? Because we’re seeing the island intersect reality incomprehensibly. If we were 2D creatures living in a 2D universe, and someone passed a 3D apple through it, we’d see a bunch of seemingly random coincidences appearing and disappearing in our universe without realizing they were part of a larger structure.
Likewise, the Island intersects all of reality in a series of inexplicable coincidences that happen to be tiny elements of the n-dimensional nature of it that we, as 3D+1 creatures cannot perceive wholly.
It’s funny, I first read about tesseracts when I was a kid in the book A Wrinkle In Time. There are a bunch of funny little coincidences between that and Lost… We’ve got travelers who can’t find their way home, scientists researching mysterious phenomena who are imprisoned by their work, a black cloud monster… but shucks, when you watch enough Lost, you start finding significance in coincidences all over the place, right? 
Anyhow, for your consideration. I haven’t seen this elsewhere yet.
Edit: Ok, and immediately after hitting save I google and find that other folks have made the same connections like at http://lostbullets.blogspot.com/2007/07/wrinkle-in-time.html
Blast! I almost liked it better when I was caught up in shows that DIDN’T have such a big audience because I had a better chance of coming up with something significant first.