I recently went to (mainly 11th-14th C) Lincoln Cathedral (http://www.lincolncathedral.com if you can handle excess Flash with no HTML alternative ) where I heard something which makes an interesting addition to this thread.

The Lincoln Imp is a famous little statue planted fairly prominently inside the Cathedral near the Shrine of St. Hugh - which was second only to Thomas a Beckett's Shrine at Canterbury Cathedral as a destination for pilgrims. As it's inside the Cathedral it isn't a gargoyle, even though it looks quite a bit like one.

The legend of the Imp is quite good: http://www.theimp.lincolnfans.co.uk/lincoln.shtml but our Guide reckoned the Imp's origin was a little more intentional and clever. People apparently used to believe in the literal truth of (a or the?) Devil being behind their left shoulder and an Angel (or God) being behind their right shoulder. This is the origin of throwing spilt salt over the left shoulder, thereby preventing bad luck (by blinding the Devil, presumably).

The Lincoln Imp sits atop a pillar on the left side of the Shrine of St Hugh. As you adopt the position of a pilgrim, kneeling before the Shrine, a glance up and to the left reveals the Imp looking down at you, one leg casually crossed over the other, waiting for you to slip up (check the Imp link above for a pic). In other words: "Watch it, mate - you're nothing special even though you've made this great pilgrimage. Get holier-than-thou, and I'll have ya!" Our Guide added that Lucifer fell through Pride, making this perhaps the greatest sin.

Lincoln Cathedral is awe-inspiring, BTW. As our Tour Guide said more than once, without overstating his case: "We think we're clever".