I always draw the ER diagram by hand first. If you run through the every table one after the other and examine the relationships every relationship will be listed twice so there is an inherent double check on every piece of information. I typically sketch the ER diagram on banner paper or randomly tape together several sheets of paper when extra space is needed and frequently redraw the diagram highlighting the essential relationships, adding notations and possibly dropping relationships related to summary and lookup calculations (they add noise to the ER diagram).
In my experience most software based ER diagramming tools are difficult to understand if they run automatically and just spit out a diagram.
