I've not seen these ideas discussed elsewhere (but frankly I'm too lazy to look much farther than the first 20 comments on Pajiba), so here are some randoms:
1. Jack recognized Desmond not because his mind is splintering, but because they have met before. When Jack was running up and down the bleachers in that stadium, they chatted briefly. Long before Desmond went sailing around the world. AND HOLY MOTHERFUCKING SHIT, YOU GUYS!!!!! DESMOND IS WEARING A WEDDING BAND! You only catch it in a couple of frames, when he's standing to let Jack into the seat, but it does flash brightly.
2. But maybe Jack's mind really is splintering, a la Daniel Farraday and Desmond Hume.
3. Fake Locke / Smoke-Monster wants to go home. He is, however, hundreds of years old, so home cannot be so simple as "Paris" or "Madrid". It has to be some place unaffected by the passage of time. Hell? Possibly. Heaven? Equally possible. If so, then Jacob is (was) either an angel sent to keep him trapped or a demon sent for the same purpose. Odds seem likely that Jacob was an angel, given FL/SM's conniving efforts to escape through the centuries.
If FL/SM is a demon, and the island was an energy prison of some sort, that would explain the need to continuously move it, as God would seek to protect man from the evil, yet man's fall from grace would also explain the continuous need to seek it out.
Sorry to drop the obvious heavy-handed religious themes here, but either Damon Lindelof and Carlton Cuse are the smartest two guys in the whole history of story-telling, or it's gonna go Matrix on us. I don't see any other way out.
4. Richard Alpert. FL/SM said he was glad to see him out of those chains. Was Alpert a slave on the Black Rock? This I have seen covered, but it seems unlikely to me. I've long thought Alpert was a crew-man on the ship, that Jacob was its captain, and that at some point there was a serious mutiny. There are not other "others", but two groups that can both trace their history to that one ship. Those who served, and those who mutinied.
5. The split time-line. I can't be the only person who noticed that the 2004 non-survivor passengers are being forced together in spite of their good landing. There are threads tying them all together, and I'm curious to see whether or not they need the island physically to be forced into interaction. Perhaps the differences in the alternate time-line were imposed by whatever energy/spirit/whatever in order to produce the same results. Sort of a manifest destiny, if you will.