I'm of the possibly unreasonable opinion that books and rules do not break up friendships... people do. [/COLOR]
While that is true, I wouldn't underestimate the impact of a edition Wars on friendships. Roleplaying is an inherently intimate hobby -- you spend a lot of time together in a shared imaginary space, often sharing relatively personal aspects of yourself via the mechanism of your character. As such, something that creates a wedge in that activity can also create a wedge in the friendship.