From a role-playing view, I think Witches and Sorcerers are the classes that fit words of power best. I'm running a non-Golarion pathfinder game, but none of my gamers are interested in the WOP yet. As for advice, anyone that uses the words of power (especially spontaneous casters) should put together a short list of 'common' phrases they use most often, and have them ready so you don't have to sort through the entire list and slow down the game in the middle of combat.