I tend to take humor too seriously. That is, sometimes, I'm a little obsessed with what is funny, when, and why. And in being so, I tend to suck the funny out of things sometimes. Which in itself is rather interesting when you think about it... Or, at least, when I think about it.
That being said I would suggest that humor, when used carefully, can be a great way to get your point across.
Let's take that aforementioned Planescape quote. In my experience, Planescape as a setting is rather, well, brutal. And Crothian's quote is very representative of that fact. While it is funny, it's also telling you, "In this place, you can die over the slightest thing, so watch you step pal."
HoL is a whole other story. (hahaha hehehe) I have a signed copy of HoL, I love that book, we actually played it once. But the point of it was ONLY to be funny (Do you want a cookie? I baked them myself.) and anything that could be used to actually PLAY something that resembled an RPG was a happy accident.
Even if you're trying to produce something like Toon, GURPS I.O.U., The Malkavian Clanbook, or the Principia Discordia (!fnord!) you're not going to want to reach for the same level of sheer wackiness-per-word count of HoL. Because, presumably, you want to produce something that can actually be used for more then one session. (See? I didn't forget about Paranoia.
)
Two of my favorite examples of humor used well in a book that isn't especially supposed to be humorous are in White Wolf's "Laws of the Wyld", which is the book of rules for Werewolf LARPing. The back of the book starts of with "Take back the night! And the afternoon, and midmorning..." It was something of an unexpected departure from how they normally presented their books (in the text on the back) that it not only made you laugh, but it made you sit up a bit and take notice. Again, it sent a message, "Playing Werewolf can be different from playing a Vampire, so throw everything you thought this book was going to be out the window... Of course, it was actually a whole lot of more of the same, but I still like W:TA better then V:TM.
Inside that book, one of the disads was "Extreme Hatred" and the example they gave for this was, "AAAARRRG!!! I HATE EARTH TONES!"
Again, very funny, and again, it shows something important about that game mechanic. The thing you hate, can be the smallest little thing, but your reaction to it must always be huge. (No matter how incidental it may seem when it comes up.)
