humor is a very effective tool to get people to actually read something though. I wouldn't use it in the manual for a space shuttle, but for a FAQ of a website with many rules? Please yes.
It's effective as long as you're communicating with peers. Anything beyond that and someone will complain that it's not funny, it's belittling, sarcastic, rude, discriminating...etc.
Ideally that would still mean people read it, but in practice it seems that as soon as someone put out the label, no one really cares anymore about what's written ;)
There is a crowd I want to reach with documentation, and there is a crowd that can smell their own farts all day for all I care. I'm not going to tailor documentation towards the latter group.