Lets not get carried away and break them up sooo much that one subforum will have 2 topics and another will have 400. I say a subforum for "All Humor" would be sufficent. With just a tad over 500 active members I don't think we have the ability to fuel multiple child folders for just "humor" on a powerstroke forum. Now, if we had 20,000 members I could see 5/6/7 subfolders.
Reason I say this? We did something similar on
www.brickcity.net (I'm a Moderator. but I'm best friends with the Admins since all 4 live in my town) and all but 1 of the folders fell inactive very quickly.