I have to agree with you on many cases — but I would take exception for the most successful attempts, namely this year: Google Maps’ Pokemon hunt, and a couple others.
When operated by communication offices with little contact with the company’s culture, like most attempt, it falls flat. Otherwise, those can be very representative of a company’s culture, and I would recommend checking their last prank before applying to a company (if you expect to have the luxury to choose). It you think it’s funny, edgy, or demonstrate an expertise, than yes, you might be on track.
A couple of GMail’s pranks have been illustrative of that: creepy to people without knowledge of databases, yet funny because obviously non-scalable to people familiar with large on-line structure.
Humour is by far the most revealing element of anyone’s culture, and that’s why I like questions like ‘Tell me a joke’ during interviews — although, to be honest, I’ve only asked it when being the interviewee.