Found through Tall Skinny Kiwi, The Mystery Worshipper:
Ship of Fools has an intrepid team of Mystery Worshippers travelling incognito in the British aisles and beyond, reporting on the comfort of the pews, the warmth of the welcome, the length of the sermon... The only clue that they have been there at all is the Mystery Worshipper calling card, dropped discreetly into the collection plate.
I think I've only attended one of the churches on the list.
That is an excellent website. I wish I could get them to come to my church, though that guy might be pretty easy to spot in the Lone Ranger mask.
Were you the mystery worshipper for that church you attended?
No, that wasn't me! ;)