www.elfontheshelf.co.uk/?from=elfontheshelf.com
It's an American idea (of course ) that's jumped across the pond. This is the official site. There are lots of "traditions" connected to the elf, including the one mentioned in the survey, of elves creepily reporting back to Father Christmas on a child's behaviour. Also lots of expensive accessories and geegaws to part you from your money.
We don't do any of that. I bought a couple of elf dolls a couple of years ago from Amazon for about £4 each (Tesco sell them now). From 1 December they appear in the DGC's houses every morning, doing something naughty (swinging off the Christmas tree, making snow angels in flour on a baking board, dipping a rod into the fish tank, etc). The little ones love looking for them every day, the parents get a little bit tired of the damn things and are glad when they disappear on Christmas Eve.