I attached a link to another article from Let Us Reason.org here. I think they summed it up very well, with a lot of references to scripture and other books.
The whole being slain in the spirit thing is I believe demonic as it is not mentioned as being used by any of the apostles, disciples of even by Christ himself. The references in the bible about people encountering God's presnece doesn't reflect anything like what is seen in most revival meetings, like Benny Hinn, of whom I have no use.
I have also heard of the story of Annias in Acts ch.5 being used as reference for being slain in the spirit, but that was taken out of context. They were literally SLAIN by the Holy Spirit. The lied to God and were killed because of it.
I do believe that God's presence can manifest so heavily in a person that they cannot stand. They might fall to the ground, sit down, I don't know. I don't think anyone can really do anything in the manifest presence of the Lord.
What I don't believe in is what is done at church services now days. Herding and lining people up like sheep to the slaughter, literally. If it is really God, why do they have to be lined up, why do you have to touch, push, shake or blow on them. Why do you have to say anything?? If they need prayer, wouldn't it be enough to stand in agreement with them in prayer, and if God manifests His presence on them great. If they fall backwards, let them fall, God loves His children and if it is really Him, I don't believe He will allow a person to be physically hurt while in His presence.
Most of the references in the bible, particularly the OT, of people encountering God's presence, fell face forward, in an attitude of submission, worship, etc. Most of the time when this happened, it was God's judgment, or revelation going on. Obviously God can still judge and reveal to whom He pleases. My issue, is why is this "the norm" for Charismatic churches????