One thing I haven't run into, at least to my knowledge, is clear cut demon possession - not of the kind that Jesus' disciples encountered when he sent them out.
I've always attributed it to the fact that we are not (I am not) as attune to the spiritual realities as the disciples were (and there's certainly something to that). I'm not saying it's correct, but we've come to rely on scientific/medical explanations for what may be demonic.
Jonathan Edwards raises another possibility in a sermon from 1736. It's a sermon he preached for a young pastors ordination based on the passage in Luke 10:17-18, "17 The seventy-two returned with joy, saying, “Lord, even the demons are subject to us in your name!” 18 And he said to them, “I saw Satan fall like lightning from heaven."
In his explanation of the passage (Puritan sermons were often broken into three parts: Explanation, Doctrine, and Uses or Application) Edwards comments, "In those days when Christ was on the earth, there were multitudes in the land possessed with devils, which seems to have been so ordered to prepare the way for a glorious triumph of Christ over the powers of darkness in casting them out."
When you look at the Old Testament you see no clear examples of demonic possession. The troubling spirit sent to assault Saul may be the lone exception (1 Sam 16:14). During the intertestamental period we do have accounts of Jewish exorcists, especially from within the Essenes sect and also in other pagan religions. Then, all of the sudden, a flurry of activity around Jesus' ministry, continuing on to some degree in the early stages of the church (though not with nearly the frequency in Acts as you see in the gospels).
Edwards point makes sense to me on two levels. First, Satan knew of the coming Messiah and his attacks and activity were intensified in the period around Jesus' coming. Second, this was according to God's plan so that Christ might display his power and the inbreaking of the kingdom in awe inspiring ways. Standing there watching possessed pigs run off a cliff you couldn't miss a) demons destroy, b) they fear Jesus, and c) he could destroy them any time he wants.
Conquering King indeed!