The only place I've really seen a rep style system really work is in the stack exchange group of sites such as stackoverflow. Sure, you *could* still get rep for making a quirky joke in an answer, but if you do there's a greater chance you'll lose rep for it because that sort of thing should belong in a comment (which you don't get rep for anyway.)
It's better than using the post count as a measure, and I still think it has it's place - but only just. It's certainly not a fine grained method of distinguishing if one member is more knowledgeable than another.