There's alot of debate as to whether the Man in Black is infact the smoke monster. Since the finale, I have believed them to be the same entity, but there are others who believe them two seperate entities. Evidence is there for both sides, but no proof yet.
-In the season 3 recap episode right before the finale, Yemi, Kate's Horse, and Christian Sheppard were confirmed smoke monster material. So we know as a fact that the monster appears as others, human or not. -Ben's encounter with the monster instructs him to do what ever Locke says. Locke wants to kill Jacob, therefore the monster wants to kill Jacob. They are atleast on the same side if not the same. -When Ben summons the monster, it does not come. Though Flocke comes out of the jungle after Ben says dead is dead. -Before the monster appears to Ben in the temple, Flocke leaves, once again showing the two never in the same place at the same time. -Flocke also knows where Ben can find the smoke monster, which he does not.
These are the notes I've found, all connecting (mostly) to MIB and Smokey being one and the same. If you think they're seperate, please comment, as I'm looking for reasoning, as while I hope, I don't have the answer yet.