The best thing about Planning Assumptions is that you get to ask the question to the planners, "What is your Branch Plan when your Planning Assumption X is shown to be false? Have you war-gamed that?"
Depending on the nature of the Planning Assumption and the depth of the planning - responses can be interesting. One thing you don't want to hear is, "We find that highly unlikely." - and then you have to remind them, "... then why do you have it as a Planning Assumption?"
I'm pondering the above over at USNIBlog, come visit.
