nice job.
did you mention that people can also use sql injection with getvars? like
stuff.php?id=1
stuff.php?id=1' OR '1'
also, i have a question, is it possible to inject sql using cookies? like if they have
"SELECT * FROM users WHERE username='".$_COOKIE['username']."'"
you could change the value of the cookie to contain sql in it.
just a few pointers
