I think I kind of like how this thing lets you do either quick ASCII art diagrams or embed graphviz (via Gravizo). The syntax for inserting Gravizo diagrams isn't too bad:

  ![Figure [graph]: A more complex graph example](http://g.gravizo.com/svg?
    digraph G {
     main -> parse -> execute;
     main -> init;
     main -> cleanup;
     execute -> make_string;
     execute -> printf
     init -> make_string;
     main -> printf;
     execute -> compare;
    })