I haven't heard anyone else mention some of these things so I thought I'd just throw it out there. I'm definately going to be using the word "assume" a lot, after all it's called a theory for a reason. Also, I'm going to run off of the assumtion that Smokey and the MIB are the same thing. I'm aware that that's not much of a popular theory among many, but that's just the direction I'm taking.
First of all, we know that Smokey is most likely thousands of years old due to the fact that he lives in a shrine in the ruins of the temple. SO given the assumption that Smokey and MIB are the same thing it only seems natural to draw the conclusion that the Man In Black we saw talking to Jacob in "The Incident" was just another body in a long line of bodies that Smokey has used to communicate with the living. Assuming this is true, which I know is somewhat of a leap, I would say that Jacob killed the Man In Black a long time ago and Smokey has been jumping from body to body (Christian, Yemi, Alex etc) ever since manipulating everyone, more specifically Ben and Locke, to reach his goal of killing Jacob and then who knows what else. This is obviously why Richard wanted to recover the bodies of the Others that Sawyer killed in "Lafleur" as well as Amy's husbands body. He didn't want Smokey to be able to use them for his evil purposes. And how he would have disposed of the bodi! es could very well relate back to why Flocke pushed Jacobs body into the fire after he died. Could burning the bodies mean that they can't be brought back? Either way we know we haven't seen the last of Jacob, not yet anyways. Could we be lucky enough that at some point someone like Jack would die and be inhabited by the freshly released soul of Jacob? Or maybe that's what Lapidus was a candidate for. Wouldn't that be cool to see, MIB/Locke versus Jacob/Jack? That would be the battle of the century however unlikely it is.
From what I remember everybody we've seen "come back from the dead" was a person that either did or most likely did die on the island with the exception of Bens mom (and Walt but that's a different story). So what exactly was Bens mom then? From what I remember Darlton claimed she was a "ghost", but they also said Lost wouldn't involve time travel so I'm going to ignore what they said. I'm going to propose that it was Jacob taking the form of Bens mom. If we're going to assume that MIB/Flocke and Smokey are the same thing then clearly Smokey can jump in and out and back into bodies if he chooses, or take the form of them anyways, (see temple scene in Dead Is Dead). So why couldn't Jacob leave his current form and take the form of Bens mother or Walt or any of the ghosts that he wants? Think about this, all of the off-island ghosts have given us no reason to believe that they have ill intents, unlike a good share of them on the island. Personally I think that all ghosts that ! we've seen off island (Charlie, Anna Lucia, Christian, Claire) are either Jacob himself or under the control of Jacob. I believe that while MIB was trapped in the Cabin he was imprisoned on the island and could only effect on-island events, whereas Jacob could move freely where he pleased.
I'm pretty sure I've missed some things so if anyone has some critisizm or anything to add feel free to comment, just be gentle, it's my first time...