The Mystery Worshipper [Ship of Fools] – Part market research technique, part Yelp, here’s a niche example of online reviews. The headlines are gently self-effacing, with a post-modern take on reviewer umbrage, say “Cleaning lady plays iPod at Santiago el Mayor, Zaragoza.”

Since ancient times (ok, 1998), Ship of Fools has been sending Mystery Worshippers to churches worldwide. Travelling incognito, they ask those questions which go to the heart of church life: How long was the sermon? How hard the pew? How cold was the coffee? How warm the welcome?

The only clue they have been there at all is the Mystery Worshipper calling card, dropped discreetly into the collection plate.