Knowledge skills are some of my favorite skills to have in a game. When you succeed on a check you obtain relevant information about your situation. When you fail, it's hilarious. Even more so than spot or listen checks. I like to let players make stuff up when their fail knowledge checks. Or say they don't know. But it's much more fun when they play to the same style as I do and make up something completely wrong for their character to declare about the given situation, monster, geography, etc. Fun for the whole party!