Nice introduction. I agree it (the database diagram tool) the has some nice features, but it also scared the hell out of me. As I recall, when I decided to document some relationships, it wanted to create corresponding constraints in my database (which, for other reasons, I can't have.) In other words, I was left with the fear that I could much too easily change my dbs in an attempt to provide some documentation. I came away with the feeling that it was not a documentation tool, but a high level design tool. Having stumbled over the limitations of other "high level" tools (like the view designer), I decided to avoid it.
Did I dismiss it without giving it a good chance?