It is my experience that knowledge skills are unimportant(for lack of a better term). Players spend their points and, if they have a few left over, will put them in a knowledge. They are rarely important to the game and generally a waste of a skill point.
I currently use the standard method for knowledge skills; buy ranks in a specific knowledge skill and that determines your level of knowledge on the subject.
I am considering changing to a more abstract method. Players would not have to buy ranks in a subject. If it makes sense for their character to know something, then they can know it. To determine level of knowledge on a subject players use one of three methods; they use a related skill such as foraging for information about plants, gather information for information gained from people, and research for information gained from documents and other non-people sources.
I like this method because it frees up points for more directly useful skills and is less limiting. You never have to worry about your ranger not knowing poisonous plants from healing because he did not have points to spare for knowledges.
I do realize that this method could easily be taken advantage of. The GM would have to take care to make sure players are being true to their character concepts.