First off, I liked Across the Sea. To all you haters out there who want answers to everything, might I suggest you watch one of those half hour sitcoms where everything is resolved in the running time. I think that one of the best things about Lost is that, when it's all said and done, there will still be unanswered questions. By doing that, it ensures its own legacy, as well as giving us more to speculate about. That's right, Lost is the gift that keeps on giving.
Anyway, back to what I wanted to say, learning more about Jacob and MIB made me want to go back and rewatch the scene when we first met them in The Incident. The main thing that I focused on was the whole exchange between Jacob and his brother regarding whether people would always come in to destroy, or whether all of the prior destruction was building up to a final destination.
This was interesting because MIB takes on the pessimistic ideals of her mother against humanity, showing that his soul had tipped against humanity and had become dark like hers. On the other hand, Jacob is seen putting his ideas of progress into work by spinning the yarn for his tapestry not manually, but rather with a foot-operated spinner. The fact that he was weaving, however, seems to show some of the facets of his mother. The meaning of this could be that the crazy mother was the complete protector and judge of the island, while her sons split the duties she held. Ultimately, it HAD to be Jacob because the darkness in MIB's heart had lead him to not care for the island enough for him to protect it, while Jacob's overall good nature and desire to see the best in people would have impaired his work as judge, something which the disembodied Smokey obviously has no problem with.
Anyway, this post went longer then expected, but let me know what you think...