When creating a new course on a moodle site, the Summary field is already filled with the default text "Write a concise and interesting paragraph here that explains what this course is about". This is not the correct way to do it. On large moodle sites, where a large number of courses are created semi-automatically by an admin, the exact description of the course is often not available to the admin. This results in the default text being displayed next to the link to the courses in the courses list on the front page of the moodle site. Obviously, this text is meaningless to the students who peruse the list of courses.
Fix. I suggest a) removing the default language string in the course summary and of course b) removing the "required" rule.
Patch: in file course/edit_form.php, remove those 2 lines:
// $mform->setDefault('summary', get_string('defaultcoursesummary'));
// $mform->addRule('summary', get_string('missingsummary'), 'required', null, 'client');

Joseph
PS.- See this discussion on the French course forum: http://moodle.org/mod/forum/discuss.php?d=91474