Primarily yes, but it also seems to have occurred, oddly enough, when demons were annoying or just got in their way.
The attitude of Christ and the apostles toward demons in the NT is quite unexpected, perhaps due to our pop-culture, Roman Catholic apprehensions of their natures, to which I believe Bayou above alluded.
No dramatic showdowns, no Frank Peretti-type spiritual battles; just kind of a... weary contempt, if I could put it that way.
Interesting. I never noticed that before. My own take is that 90% of "demonic issues" can be dealt with (by the Christian, anyway) simply by getting rid of garbage in your life.
I do believe what we normally think of as "exorcism" can happen today. There is no logical reason why it can't (and certainly no Scriptural reason why it doesn't). I just don't think it is normal. The link by Heiser explains a lot on this.