I even go so far as to write up information sheets containing esoteric information known only to sages in a particular knowledge skill--a player who drops 5, 10, or 15 ranks in a knowledge in my campaign will see tangible results when I hand him a piece of paper with hard, useful data on it. This, in turn, aids roleplaying, as players in the know share their knowledge with the rest of the party as the situation warrants. A player who feels like an expert on a topic is a happy player. I want that.