I admit that I don't know everything about subject-matter experts or SMEs (rhymes with please). But I do know that there are some things that you should avoid asking SMEs, the main ones being 'Does the user know this already?' and 'Do I need to explain this to the user?' The problem with these questions is that the SME is likely to reply 'No!' to both of them when in fact the answer is most definitely 'Yes.' SMEs tend to believe that everyone knows as much about technology as they do. Never, never, never let the SMEs tell you how to write the documentation. A SME is the subject matter expert, not the documentation expert (that's you).