I agree that we shouldn't assume that the smoke monster has anything to do with the apparitions...or even that it is necessarily a monster. Throughout history people have created beasts to scare and thus have control over others. I would not doubt that this is the real purpose of the smoke monster. As for its physical abilities, well, I am not sure how to explain that yet.

The appearance of dead or supposedly dead individuals on the island is another way that Lost attempts to blend the real and surreal or fantastic to the point that we are not sure which is which...or maybe both at the same time. One thing we know is that these apparitions usually come in 2 kinds. They are either symbolic of a characters inner demons (Christian to Jack, Yemi to Eko, Hurleys imaginary friend, etc) or they come to advise or guide other characters (Charlie, Boone, etc). I think some of it is ghosts taking advantage of tears in the space/time continuum. Other times, I think it is guilt manifesting itself. I don't think it's Smokey though...