I haven't read anything yet, but I bet the theory that the cliffside cave belonged to MiB is pretty avid right now. Here are my thoughts on this:
First of all, I don't believe that MiB ever said that the cave belonged to Jacob; I only remember him saying "Jacob has a thing for numbers". So naturally, not knowing there was a lighthouse, we assumed that since Jacob's candidates were on the wall of the cave, it must have been his.
Then there's the fact that the cave belonging to MiB and the lighthouse belonging to Jacob fits in perfectly with the opposing imagery associated with the two nemeses (and maybe some that isn't yet associated with them):
1. Order vs. Chaos: The Cave has candidates written in random order, with varying sizes and facing different directions (upside down, sideways, etc.). Whereas in the lightouse, the names are written neatly in numerical order around a circle.
2. Light vs. Dark: The cave is dark. The lighthouse emits light.
3. High vs. Low: The cave is deep underground. The lighthouse is a tall building
4. Guidance vs. Manipulation: MiB leads Sawyer to the cave in order to use the information it reveals to manipulate Sawyer and try to utilize him as part of a specific agenda. Jacob leads Jack to the lighthouse to let him discover his future path
5. Patience vs. Impatience: MiB is eager to get off the island. Jacob is willing to wait patiently for Jack to "look out at the ocean" until he is ready.
Are there any others? Please share!
By the way, I gotta give props to this season. In my personal opinion we have had three among the most TITANIC Lost episodes in the first four of season 6. Amazing stuff. Sheerly amazing stuff.